[Bullitt]

It's common on photography forums to indicate whether or not you want others to borrow your images and repost their own edited versions. However it is considered in good taste and out of respect to ask beforehand every time. I frequent a couple different forums where longtime professional photographers post and this seems to be a common thread between them. Always ask, and always give credit with or on the image.
I personally don't care who does what with my images. I'm not aspiring to be professional or anything. If someone enjoys my photos and wants to put their own spin on them, great have at it I'd love to see your work. Though I would take issue with someone stealing my photos (representing them as their own).