The following sites, are arranged by the major phyla of living organisms. The images can be used directly on a computer screen or can be printed on paper or transparencies for use in the classroom. Fungi and Lichens are also included, but are shown after the Flowering plants.
A good way to search for images is by clicking on the image search icon on Google. Usually a large number of thumbnail images appear and you can select from  them.

A site that is well worth visiting is the teaching image collection of the Botanical Society of America. There are currently 14 sets of images grouped under a variety of headings including Plant Geography, Plant Morphology, Plant Defense Mechanisms etc. The images come in three sizes, thumbnail, medium and high resolution. 

http://images.botany.org/

Two other valuable sites are the Botanical image site at the University of Wisconsin,
and the Stanislaus Botanical Image Database.

http://botit.botany.wisc.edu/

http://arnica.csustan.edu/botany/index.asp

Many specific references are made in the groups below.

Cyanobacteria

Cyanosite
This is a webserver for all aspects of cyanobacterial research. It includes an excellent photo gallery , links to bibliographies and cyanonews.
 
 

University of California, Berkely
There are not as many images on this site, but it has links to some good sites on toxic cyanobacteria, ecology of cyanobacteria and nitrogen fixation
 
 

Eukaryotic Algae

BowlingGreen State University
There are more than 185 digitized images of diatoms on this site, including some scanning electron micrographs.
 
 University of Wisconsin Chlorophyta
A good collection of green algal images

Susquehanna University algal image archive
The images on this site are listed in alphabetical order, and include diatoms, green algae and dinoflagellates
 
 

University of California Red Algae site
This site has some clear images of membranous and coralline red algae as well as some general information on the group
 
 

Biology Department, Indiana University
A good general introduction to diatoms, with some images.
 
 

Seaweeds. National University of Ireland
Many good images of common seaweeds of the northern temperate part of the world
 
 

Harmful Algae page
Good photos of a variety of red, brown and yellow tides, together with photomicrographs of the organisms which cause them. This page is produced by the Woods Hole Oceanographic Institute
 
 

University of Calgary. Dinoflagellate site
Excellent pictures of dinoflagellates, which can be enlarged. Also includes some general information on the organisms.
 
 

Freshwater Dinoflagellates
This site has some excellent SEM photos of freshwater dinoflagellates from Ohio. There are also links to other dinoflagellate sites as well as some scanning electron micrographs of other algae.
 
 

Oceanlight Kelp forest photos
Some excellent photos of giant kelp forests off the coast of California. Close-ups showing the structure of Macrocystis

Cytographics
A wonderful site developed by  Jeremy Pickett-Heaps.  Diatoms and algae are featured along with cell biology.
 
 

Bryophytes

University of Glasgow, UK.
This site has a collection of liverwort photos, which are quite large and clear.
 
 

University of Wisconsin Bryophyte Image site
This is a really excellent source of teaching images, which includes photos of Anthoceros sporophyte features (stomata and pyrenoids). There are also some wonderful micrographs of sectioned material very similar to slides seen in general botany courses. In the liverwort section, both Marchantia and Riccia are featured
 
 

Ohio University Bryophyte Home Page
Both information and photos of liverworts and mosses are shown on this site. The photos are not as large as on the previous page but they are of good quality.
 
 

Mosses and Liverworts in Wales by Alan Hales
A large number of species of both mosses and liverworts are shown on this site. There is also some general information on bryophytes and some excellent photos of bryophyte structures.
 
 

Seedless Vascular Plants

Psilotum

University of California, Museum of Paleontology
This site has some general information on Psilotum as well as some images
 
 

University of Hawaii
This page has some good thumbnail sections of Psilotum, which can be enlarged. The sections are also labelled.
 
 

University of Hawaii
This second page also has thumbnail photos of living plants, which enlarge well.
 
 

Club Mosses and Fossil Lycopods

University of Arizona Catalogue of Pollen and Spore images
Excellent scanning electron microscope images of Lycopodium and Selaginella spores. 
 
 

Texas A&M University Vascular plant Image Gallery
The Vascular plant image gallery is a wonderful collection of photographs, and it will be mentioned again on this page. Look for photos of several Lycopodium species as well as illustrations from monographs. Species of Selaginella are also illustrated.
 
 

University of California, Museum of Paleontology
Some general information on lycophytes, complete with a picture of a fossil lycopod, Lepidodendron 
 
 

College of Science,Southern Illinois University/ Lycophytes
Excellent photos of living material, plus photomicrographs of cone sections. Both Lycopodium and Selaginella appear on this page
 
 

University of Wisconsin/Lycophyte site
Good coverage of both Selaginella and Lycopodium, general information together with photos and photos of sectioned material.
 
 

                                  Cyanobacteria | Eukaryotic Algae | Bryophytes
                        Seedless Vascular Plants | Club Mosses and Fossil Lycopods
                         Horsetails | Ferns | Gymnosperms | Flowering Plants | Fungi
                                                                    Lichens

Horsetails
 
 

University of California, Museum of Paleontology
This site has general information on Equisetum, as well as a couple of images.
The second site has some good fossil representatives as well as more information
University of California, Museum of Paleontology II
 
 

University of Wisconsin
The images here are suitable for a general botany course, some are labeled and there photos of gametophytes .
 
 

Ferns

University of Wisconsin
This site has some general information on ferns, accompanied by labeled images and a life cycle diagram. Following the general information there is a list of fern genera, with descriptions at the end of which are some wonderful images of the plants.
 
 

C-fern Site
An excellent site for teaching purposes. C-ferns will be mentioned again on this page, but there are some good photos of various stages in the life history. If you are using C-ferns in your course, these will be a valuable teaching tool.
 
 

Color images for the flora of Roosevelt Monmouth County, New Jersey
Ferns and fern allies are shown on this site,so you will find Equisetum, Lycopodium and Selaginella. The fern images are also good showing the different parts of various fern species.
 
 

Gymnosperms

http://www.resnet.wm.edu/~mcmath/bio205/links/gymnosperms.html
This site has a good collection of links to other sites including The American Conifer site and the PNW Conifers - Mystery Tree page. 
 
 

Royal Botanic Gardens, Sydney. Wollemi Pine site
Some excellent photos of the Wollemi Pines discovered a few years ago in Australia
 
 

Texas A&M University Vascular Plant Image Gallery
Cupressacae. Photos are of whole plants, leaves and staminate and ovulate cones.
Pinaceae. Images of whole plants, leaf clusters and cones
Other Gymnosperm families may also be searched for here
 
 

University of Notre Dame Cycad site
There is some general information on cycads at this site, and some good pictures of Encephalartos, whole specimens and cones.
 
 

 Bristlecone Pine Site
This site is packed with information about the bristlecone pines and includes a photo gallery of specimens, as well as extensive links.
 
 

University of Wisconsin
An excellent site for photos of whole specimens, leaves and cones. Search the directory for the family that you want.
 
 

Lichens

Flowering Plants

University of Hawaii:Images and descriptions of flowering plant families
A very extensive collection of photographs of flowers and flower parts of many families. The photographs are of excellent quality and can be enlarged from the thumbnail.
 
 

BUBL information service Plant image site

This page has 18 links to a variety of very good flowering plant image pages, including the National Plant photographic Index of Australia, the Flora of Europe,the Latin American plant Gallery, and a site dealing with carnivorous plants and their habitats.
 
 

Texas A&M University Vascular Plant Gallery
Extensive representation of many flowering plant families. Good photographs. Search the index for the required family.
 
 
 
 

University of Wisconsin Flowering plant site
A marvellous site for plant taxonomy courses. Following a series of links, through the classification scheme, you finish up with photos of dissected fruits, leaves, leaf venation details of representative genera.
 
 

Fungi

Tom Volk’s Fungi Site at the University of Wisconsin
This is a very complete and interesting collection of photographs and also photomicrographs of fungi. The photomicrographs of mycorrhizae are labeled and particularly clear and easy to understand.
 
 

Mycological Society of America Slide Collection
A really beautiful and extensive collection of photos. There is a separate listing of the photographs, which have been taken by a number of mycologists and then the photographs themselves. 
 
 

Cornell University. The fungi of the Lindsay Parsons Biodiversity Preserve
The fungi at this site are listed alphabetically, and not all the listed species have photos, but there is a long list, and the photos are good and clear.
 
 

Michael Wood’s Mycoweb
This is a very extensive site, with a large collection of photos, and also links to many other sites with photos of fungi. In addition you will find recipes for a variety of fungal dishes! 
 
 

Chilton’s Fungi photos
This is the personal collection of Rob Chilton’s fungi photos. They are mainly of macroscopic fungi and include some of the jelly fungi.
 
 

Oregon State University Introductory Mycology course
The site has some useful images for this level of course, as well as links to other sites. The pictures are grouped into macroscopic and microscopic forms and has some good photos of ectomycorrhizal structures
 
 

George Barron’s Fungi of Canada East
A really good collection of fungal photos, shown in thumbnails which can be enlarged.
 
 

Lichens

North American Lichen Project
A collection of really fine lichen portraits is found on this site. The photos are really clear and colourful.
 
 

Oregon State University’s LichenLand
This site is really about how to have fun with lichens! There are some good cartoon drawings as well as photos.
 
 

University of Wisconsin Lichen Images
The lichens are listed in a parent directory under morphological forms. The images are excellent.