There are a number of ways of presenting illustrations. For print media, they are --in descending order of desirability -- 1) line drawings; 2) shaded drawings; 3) grayscale photos; and 4) color photos. I rate drawings higher than photos because it’s easy to eliminate noise – you simply don’t put it in. Line drawings are also better than shaded drawings because they reproduce well in all sorts of formats. Sling a line drawing on a copier and you get a crisp copy; do the same with a shaded drawing and it’s liable to turn out patchy. I like black and white photos better than color because of the same thing – if you reproduce a color photo as black and white on a copier, you lose definition.
With the advent of PhotoShop and other software, it’s much easier to manipulate photos, of course. The problem there is that you run into ethical and sometimes legal issues, especially if the photo is not yours or if the content is compromised by the manipulation. So, I prefer to keep it simple when possible and use line drawings. Since we’re talking about photography, though, we’ll simply pretend that drawings don’t exist,
For electronic media, most of what I said above still holds, except that you needn’t worry about color in terms of reproduction, so color and grayscale will swap places. The only problem with color in this context is the fact that color hue and intensity will vary from screen to screen, so you can’t be subtle. Use strong tones.