Scan them at minimum of 300DPI, preferably 600DPI.
Don't edit them in paint as it autosaves to 96DPI and you screwed.
If you can't edit them, just upload the high resolution scans as raws and ask someone to edit them.
On the other hand if those are made from images downloaded from internet and that is why they are low res, then they are pretty much useless, so try to find better and higher resolution source material.