findimagedupes is a command-line utility which performs a rough "visual diff" on two images or a whole tree to detect if any look similar. It can produce output suitable for driving GUI front-ends. It can also export a GQView compatible collection file, so you can deal with the duplicates visually. On common image types, findimagedupes seems to be around 98% accurate.
FREEdraft is a 2D mechanical CAD program. You can draw points, sketch geometry, segments and arcs to precise dimensions, and label items with text. You can trim and edit geometry, incorporate colors and linestyles, and then save your drawing. Importation of geometry from DXF files is now supported as well.