I can't speak for the women who post pics but some thoughts on your post from a guy who hasn't even posted a g-rated pic .
Yes they have their fans but I seriously doubt they'd reject a new one.
Some are unattainable for the reasons you say *sigh* but who knows you might strike lucky and find someone unattached, right on your door step.
Why would they be interested ? Have you ever known a lady who doesn't like to complimented on their beauty ? and a lot will show their appreciation with a reply.

I was like you didn't know if I should post or not then some of the pics just grabbed my attention so much I had to show my appreciation, after cleaning the drool of the keyboard.