Can someone recommend a free simple photo editor with a tool that blends a specific details I don't want to be seen?

Not exactly sure what you're looking for but sounds like you want to retouch something out of an image? If so almost any photo image editor now has some sort of basic "clone stamping" features. Or you could manually paint it out by hand with standard brushes. GIMP would work in either case...

Or are you trying to make it disappear like a "predator type" illusion where its not camouflaged but blending in... If that's what you want you would need to give more details because there are several approaches both 2D and 3D and depends on level of detail and lots of other things.