well... a stock image is basically just a normal picture... it's actually a term in making graphics.
in making a graphic, you can use a render (something with transparent background) and make your own background ORmanipulate a stock image (a picture ) by adding some effects to it OR you could mix it up, use a render of a character and use a stock background.
samples:
this was made from a picture / stock image from this thread:
this was made from a render of carnage (spiderman)
I do know this - xenforo dropped the ball by not keeping the vbulletin reputation comments as a feature. The loss of the Reputation comments data when we switched to Xenforo really was the death knell for the site when it came to all the users that left. I know I missed it so much and I got way less interested in the site when that feature was gone and I run the site.
I'm on a page about incorrect corrections, and spent the better part of like two hours trying to get someone to understand that -5^2 = -25, not 25, and then that post had comments get reposted because that group is self sustaining, and that person was in turn trying to explain what I just explained to them. And I'm taking that as a victory