Taking photos for identification
Different views
First of all, decide what type of fungus you have because it is important to provide a clear view of the part of the fungus that produces spores e.g. gills, pores or teeth. Don't just take a photograph from above, get down and take shots from the side. Don't be afraid to pick one or two specimens to arrange in different orientations. If at all possible, cut a specimen in half from top to bottom to show internal features - this will help identification no end. Try to take photos of an age range of fruiting bodies if possible to illustrate changes in colour and texture with maturity.
Habitat
It is very useful to show the habitat clearly, especially in or on which the fungus is growing. For example, if you find a mushroom growing in a woodland, take a general shot of the woodland so that people can see whether it is deciduous or coniferous, oak or birch etc... This general habitat shot doesn't have to show the fungus. Take a photograph of what the fungus is growing in/on e.g. a decaying stump or base of a dead bracken frond. If you don't have habitat shots, this information can be written down and provided with your photo.
Photo quality
Think about the composition of your shot. Make sure the fungus fills as much of the field of view as possible and is in clear focus. Nobody will be able to identify a small blurred disk in a lawn! You should check that the colour balance of your image matches your original observations. Most photo editing software allows you to adjust the colour balance.
Examples
The photo below/right of Cortinarius traganus shows immature and mature fruiting bodies. One specimen is sectioned which shows the gill attachment, veil structure and flesh characters.
Care was taken to accurately reproduce the delicate colours of this species. This species also has a very distinctive, somewhat unpleasant odour an important character to record in the field!
Also remember to note whether the colour of the flesh changes when exposed to air.
These photos of Tapinella atrotomentosa show that the mushroom has gills, has a felty stem and cracked cap surface. The first photo shows that it is growing on a conifer stump while the second shows the general habitat.
The photo below/right is a good composite shot of Suillus cavipes showing that the spore producing surface is made up of tubes rather then gills and that they run slightly down the stem apex. The cut specimen shows the hollow stem and the right hand specimen show the dry scaly cap surface. Together, these characters allow very accurate identification of this species.
By picking smaller specimens of this Hydnellum aurantiacum (below/right) and positioning them on the larger specimen the shot shows the variable shape of the fungus and the contrasting colours of cap, teeth and stem. This shot of could have been improved further by cutting one of the smaller specimens in half.
Habitat and substrate is very important. This tiny specimen of the club fungus Typhula quisquiliaris is shown growing on the base of a dead bracken frond. The macro shot also shows that the hairy stem is distinct from the smooth spore producing area above.
The error of this photograph is that there is no way to determine the actual size of the fungus. A coin, ruler or other reference would have clarified this.
Further useful information on both photographing and painting fungi can be found on the British Mycological Society and Wild About Britain sites.