Every once in a while I get questions about whether someone can use an image of mine. And the answer is always yes; I'll allow pretty much anything as long as people ask nicely and promise to give me credit.
But you don't actually have to ask in most cases. I've put all my photography work under a Creative Commons license. This is detailed in a block somewhere down on the right-hand side of the deviation page (if it's not there for one picture, I've probably forgotten to click the checkboxes. Please notify me so I can add it).
This is a link that will lead you to a really, really simple page explaining what you can do (anything) and under which conditions (give me credit; allow others to do the same). It's this page here: creativecommons.org/licenses/b… Please give it a quick read. It's shorter than this journal. There are also translations to other languages if english isn't the one you speak best.
If these conditions are okay for you, then there is no need to ask me - though I'm always happy if you tell me. Of course, if these conditions won't work for you (for example because you want to use my picture as part of something big and complex that you can't or don't want to put under such a license), or you're simply not sure, then asking for permission is always an option. But in the general case, I do want to make it easy for you to use my stuff. Feel free to take advantage of that.