Online Image Editor - Ajax or Flex / Flash?

I am working on a plan to build an online image editor with just some basic functions. It should (obviously) contain a canvas working area and support the following functions:

1. Upload an image from your computer or submit a link
2. Resize image (by dragging the corner)
3. Rotate and flip
4. Drag / move / pan
5. Layering (if more then one image is on the canvas, select vertical order)
6. And very important: it should be able to do some sort of background deletion using simple edge detection.
   Images I am using are going to be mostly of fashion items so I want to be able to take off the background if its not white. For example automatically make this gray background, white: Click for image - T-Shirt Black BG

I guess my best starting point is to grab some open source image editor and just use the parts of the code I need. My question is what will be better for me: Flash / Flex, or Javascript based editor. Each have some very nice implementations online, like Sumopaint, Aviary, and obviously Photoshop.net for Flash and some other good ones for JS.

Should I use Flash or go with a Javascript based solution? My gut feeling is towards JS with HTML5 coming around the corner.
Also if you recommend Javascript, can you please include your preferred framework for something like this??

Ajax version would have to use something on the server processing the images, like the GD Library or ImageMagick. With flash you/flex you could do the image processing on the client side, and with Flash Player 10 you can take advantage of Pixel Bender for image processing. I guess it depends on the size of your images. I would be interesting to see a benchmark on some big images, flash vs ajax/php.