picture cleanup etiquette question

[theLoster]

I have a collection of images that I've gleaned from all over the parts of the internet. One of the things I do with some of the pictures is run them through photoshop to clean them up (stitch, recrop, color enhance, remove dust/scratches/noise, etc). I've posted some of the work I've done onto these messages boards (providing references back to the original person who scanned/posted the images as best I can).

For the most part, I've gotten a positive response to them; although one person who does some scans has indicated to me that they would rather not have their images cleaned up and reposted.

Is there a general consensus with regards to posting picture cleanups? Is there somewhere that people who post their scans indicate one way or the other how they feel about it?