resources and pictures, the soul of a cover. you can get these pretty much anywhere. really.even on wattpad.

textures, PNGs, etc can even be found on wattpad resource books. do check out tutorial or resource books by CoversGraphic or GraphicCourt they have very useful resources.

but here are some apps or websites to find good textures and pictures.

Deviantart*
Pinterest
Tumblr
Google
etc.