I am a relatively inexperienced gimp user. I was recently asked by someone to replace the logo of an existing character with a different logo while maintaining the contours of the original image e.g. muscle definition.
I could use the perspective tool to position the logo on the character but it would lose the definition lines.

I read about bump maps and other tools, but frankly I'm not sure what would be appropriate for my project. I've attached an example of what I'm trying to do. In this case, I would need to replace the Superman logo with the Batman logo without losing the definition lines. This isn't the character or logo that I've been given but I think it's a good example of my problem. Any suggestions would be welcome. Thanks

Really it is as much artistic as it is Gimp tools.

One way. Use as large an image as you can get, the bigger the better.

Paint out the Superman logo and paint in any contours: https://i.imgur.com/lSFO0P2.jpg

You can get batman logos that already have a transparent background, no need to remove one. Size that to suit, paste in as a new layer, move and rotate then apply a little distortion using the IWarp tool. Filters -> Distorts -> IWarp https://i.imgur.com/x9zR4xc.jpg

Before applying a bump map, make the batman logo the full image size, Layer -> Layer to image size. It has to match the underlying superman image (the painted in one), otherwise an offset is applied. There is no noticeable light direction so settings are simple see: https://i.imgur.com/2NWT0P7.jpg

rich: www.gimp-forum.net