This is why I require crediting in ALL cases
As you may know if you've read my DD guidelines, I will not feature anything where the artist's comment doesn't include credits. No matter how great it is! The only (!!!) exception may be if it is (very!) obvious from the deviant's gallery and userpage that they shoot and use their own images. But it would need to be very obvious, because a short line of "all images used are my own" will not do you any harm. It doesn't diminish your work and it doesn't hurt you to add it and neither does it take an awful lot of time and effort to add this line.
But the benefits to the community (that same community that awards DDs, mind you) if you do put it there are very valuable: the photomanips community is one that sees a lot of newcomers every day because it's an accessible art form with appealing results. Also, our stock and resources community makes it easy to get into manips even if you don't own a camera yourself. Newcomers tend to just jump into their new hobby most of the times, they don't want to read journals about what is stock and what is not just to find out about all the legal issues that are involved.
What it boils down to is that while each of you is responsible for your own actions, none of us live in a vacuum where our actions don't affect others. If we can set a positive example, I believe then we should do that, and give some thought as to what message others will get from how we handle crediting and copyright issues. And as DDs are such a prominent part of this site, it should now also be clear why I try to uphold such high standards when it comes to crediting/citing your sources.
EDIT: miskis reminded me of the "credits coming soon"-disease that seems to be running rather high at times. If you have the time to upload your deviation, you need to make time to put in the credits! I've seen way to many "credits coming soon" dated sometime last summer to not be annoyed at the mere sight*. I get that you're eager to get reactions on your latest work, but please be fair to the stock artists that helped you create it in the first place: they put their stock out there to be used and the credit is also a way of doing some advertising for the stocker that will reach less and less people the longer you delay adding credits! As a stocker, I react pretty allergic to stuff like that and if you put yourself in the stocker's shoes you'll see that it feels like being slapped in the face, as if the deviant is trying to say "not only did I not notify you of use, but I also didn't even credit you because my time was waaaaay too precious than bothering with this lowly stuff". I hope you catch my drift here.
*this can even lead to me using the report deviation button hoping that having your dev taken down by CEA will get through to you -- I will NOT send notes or comments when I see stuff like that because I do not care for the drama that follows such exchanges, instead I let those handle it who are paid by dA to do so.