This tutorial will tell you how to change the palette of your image so that it will look right.
Firstly you should know I used Paint Shop Pro to do this and have not tried using any other programs but the method should be similar, you'll need to know how to save the pallette of an image; in Paint Shop Pro the option is in in the Colors menu and called Save Palette amazingly enough.
Right here's an example of how I changed Painting10. Firstly I found the name of the image DromEd looks for when Painting10 is inserted. I used Thief Media Edit.
I looked for the right image which was called ripoff1. Now I loaded ripoff1 and the image I wanted to replace it into Paint Shop Pro. I resized my image to match that of ripoff1, then I reduced the number of colours to 256 (8 bit).
Now I selected ripoff1 and saved the palette as ro1, then I selected my image and chose
Colors>Load Palette and loaded the palette ro1, this replaces the palette of the image.
Now Thief will display the image properly.
I renamed my image to ripoff1.
Since the palette is replaced the colours will change slightly depending on the palette of the image your replacing, so a tip is to look for an image with similar colours to the image you want to replace it with.
Now to actually replace the image properly you need to save it in the appropriate directory. The image ripoff1 was in Obj.crf and in the txt directory so I need to put the image in the directory ...Thief\obj\txt.
I don't think I've missed anything, but if you have any questions e-mail me.
Finally, heres a list that'll help you, it is not complete however. And please that note more than just the paintings can be replaced :)