I always wanted a tool to place a polygon (even just four corners) and ability to set an aspect ratio (custom or preset like 4:3, 16:9 and A-series) and have perspective fixed image or just move vertices around (just like you expect by having a textured polygon). I would like to have this tool as a part of GIMP and a standard around light image editing tools like many viewers are. Perspective correction tools are either designed for photography or I don't really know how to use them. When you have this you can add edge detection and you're almost done to do this automatically.