I'm scared to check my stock account today. I haven't checked it in months. I'm sure I'll find people who have used my stock and haven't credited me or they are selling prints without permission. I actually think, to be safe, they should always comment where the stock came from. Even if it's your own.
Well I do first assume that the people forgot to credit the stock (i mean, if its just a little manipulation maybe not (more like a retouch), but if its a detailed manip than i assume that it is unlikely that all the pieces are of their own stock. SO I most of the time ask, or tell them they should add credits (if its obvious it is stock).
There is one artist out there where I really wonder, he is quite known, but there never are any credits. So i am very unsure.
I haven't done one for a long time, but what I do so that I can remember is this... When I save the stock photo from DA if the stockers name is not in the file name I add it when I save the image to my computer. That way when I use it I can see the stockers name right there- example 'modelbytree22byJOEBLOWSTOCK' then when I'm working on the manip I keep a notepad file open and add the stockers name & link to the text file. When I am ready to post the manip I just copy all the credit info from notepad into DA.
If I use my own stock, I don't typically mention it simply because my stock is not for use. I don't want people using my personal stuff, since I am an artist outside of DA, and my page is not a stock page and shouldn't be viewed as such. But if I use other people's stuff, I definitely give them credit for it.
I guess the point I was trying to make is that when someone doesn't credit stock or material from someone else, then it is implied (to me, at least) that the stuff is their own. To actually point out that you are using your own material (which I personally think is ridiculously redundant), says to me that you have something more to offer others, or that you are giving people the opportunity to grab said material and cut it up and use those said materials for their own. Sometimes I think people tend to sweat the small stuff, instead of just enjoying the artwork for what it is. I mean, I guess I'm just baffled people will actually look at a piece of my art, and when they don't see me credit my own material (and I always credit the stuff that belongs to others), say to themselves ("Ugh, I can't believe they worked so hard on this piece and didn't bother to tell me which stuff is actually theirs!")