I used to be description-only kind of person. The reasons for this were, in a sheet, to weed out people that didn't write well/much and to stop people just providing character-appearance Sue-porn. I've since decided, it doesn't actually do this.

When writing, people have all the time in the world and as many words as they like to generate the most flowery, avidly attentive, beauteous description of a character and, worse, their clothes*. If they feel they're being tested on writing (which can be done in far better ways), they're even more likely to do this, to prove that they can write length and description.

Images, while they do tend to be exclusively beautiful on sheets (and I'm not exempt from this at all), I think kind of draw a line under character appearance, and then you can move on: there's nothing left to discuss, so I find the image plays less of a role in the game. Apart from anything else, I find they break up a text-based sheet nicely, and simply do provide a clearer idea of what the character looks like.

When finding pictures (and I encourage others to do this in RPs I'm GMing), I get the bulk of the character sorted, then trawl Google for suitable faces. The character should be built for the RP, not to fit a pretty picture. 

When GMing, I ban celebrities (that I recognise - otherwise they're not celebrities!) because the face is well-known enough to be jarring and to confuse with the real-life person and animé, because all my settings are real-world, and animé simply doesn't look like, and in my opinion usually doesn't even approximate, actual people.

* this site isn't too bad for it, but on my previous site, players were absolute fuckers for having standard beautiful wish-fulfilmenty Sue-types. I don't want wish-fulfilment seekers in games I'm GMing: I want them in it for the story and the group.