Knife looks good. It needs a shadow, though. Otherwise it is just floating in space.
You own the copyrights to your own work unless you specifically transfer them to someone else. Otherwise, they are yours.
As for sources for illustrations, that depends a lot on just what you need and what you are looking for. The best--and safest--course is to contact an illustrator directly. But if and when you do, be sure to get a written agreement that spells out exactly what the terms are.
Still too small to read in thumbnail, but there is an obvious sign. Or two.Both are codes used in the book -- yes, subjective -- but one looks objectively like a code (it's from Edgar Allen Poe's The Gold Bug) (Which oddly could also have been a John D. MacDonald title). The other looks like an odd thing for someone to post, suggesting that it's a code -- am I giving the viewers too much credit?Anyway, I could have gone bigger on the signs, but then they would have been flat and looked "constructed." As it is, they wrapped nicely around the pole. A.A., yes, it is a challenge to construct a cover without it looking constructed. That's why I'm always looking for a single photo that expresses the idea with minimal tinkering (I'm a bit ham-fisted on my touch-ups).I'm always slightly tempted to use a blank white cover with black letters, but that would be even less professional in the long run. I'll save the sign on the ground for a future book that fits that theme.
This is an immense improvement! At least the potential reader doesn't have to search out clues. By putting the signs in the center of the cover you take advantage of the natural tendency of the eye to go to the middle of the image. Then there is the pay-off of having something there that is suggestive of a story.
AACain may have a valid point in suggesting that you may want to be sure that crime is conveyed in some way. Stick a knife in the posters or something.