After seeing Halley’s image processing tool, I came across another mature online image-processing RIA, similar to Photoshop, very powerful, specializing in bitmap work — you can open images uploaded from your local machine and edit and composite them. It even has layer styles, filters, and all that. Extremely capable, but at the same time relatively complex to operate, and fairly heavy on machine resources. Let’s just look at the results: http://www.sumopaint.com/app/
That also brings to mind the https://www.photoshop.com/ platform I saw a while back — a great experience.