I'm designing a book cover for a 'print on demand' book. It is my first 'commercial' project, and I want to do the 'right thing'. I grabbed an image off the web (via Google) to use with other elements in my concept. It looks like a stock image. I cropped, increased contrast to make it more of a silhoutte, tweaked and used the image in a semi-transparent layer of the image I'm making for the cover. I imagine this happens all the time - like re-mixing and mashing up music. My question is .. when you incorporate part of an image that someone else created and in someway integrate it into your own work, at what point does it become "your own"? It feels like we should find a way to identify the original creator of the image that I used part of, so that I can compensate him/her. But I'd like to know the "rules" or "conventions" for doing this.