Not most but a few do request pics.

I always say "No thanks".   However, I usually end up with a pic of his junk anyway.  LOL

As for face and body shots....sometimes I will get those too.  I don't need them and don't want them. I do not want the responsibility of having his pic on my computer.   Some gals may feel more comfortable knowing who is showing up at her door, though. And possible use it as part of their screening. Not sure.   For me, it doesn't matter....I screen so am fairly comfortable beforehand knowing you are a gentleman.  And you can be assured that I will treat you with respect, dignity and kindness regardless of your looks.

I have received pictures along with an introductory email, and thought it was a nice gesture.

Someone being upfront and honest about who they are is never a problem for me.

Unless you are single and will not mind your photo to be passed from one provider to another. Do you think that if provider A has your photo that provider B will not get it if provider A is a reference?
It is one thing for a provider to have your email address, but another to have a photo attached to it.
It is simply a bad idea.

I have had one or two provides ask for a photo.  One was a lady who was particular about race.  Only once has a provider wanted to see an explicit photo - a concern about size limits.  I accommodated the one asking for a face but not the other, lol.   I wouldn't have done it had there been any possibility of common friends or relatives so a good amount of background info was exchanged ahead of that.