>>2954348 (OP)
water will leech into the paper between anything you put on top and the sticky part, eventually causing the artwork to slough off unless you seal in the whole sticker and the interface between sticker and surface with varnish but eventually that'll wear off
>>2954348 (OP)
For applying to what kind of surface? Outdoors or indoors? Should it be removable? Most clear tape adhesive is much too weak and is water soluble. Sticking a sheet of clear adhesive vinyl on top would probably be fine for most applications, just make sure you leave at least 0.25" margin to prevent peeling and water seeping into the paper edge like the other guy said.