Just because someone has copied something without paying attention to copyright does not mean that the actual author loses ownership. Wallpaper collection sites are notoriously loose with this. You're doing the right thing to stop and think.
When doing a Tineye reverse image search and trying to find the actual source, looking for "oldest" is often helpful. This leads back to this by called 'waste84' — although judging by that user's (NSFW) gallery I'm not convinced it's original, despite a comment thread (including "amazing skull ..." and "thanks") that implies it. That version also has a signature in the bottom right corner — although it's hard to read, maybe... "Steve" something? Other work in the gallery has different signatures. Maybe waste84 at least remembers where it came from.
Although this is not a photograph, the above illustrates a general approach for attempting to sleuth out the original of some content you've seen illicitly copied many times on the internet. Look for the oldest — sometimes also the largest, but wallpaper frames and scaling sometimes ruin that.
As a secondary note: are you sure you want to use an image found in hundreds of collections all over the internet in your product? Why not instead commission an artist to create something original and unique to your product with the same flaming-skull motif? Maybe even... a photograph!
