Pixlr is a free, online, web app alternative to Adobe Photoshop... pixlr.com/editor/
It can perform many of the basic functions of Photoshop such as:
- resizing images
- setting a transparent background
- deleting chunks of the image with magic wand
- converting to JPEG, PNG, BMP, TIFF
- adjusting the color or grayscale, etc.
It's all FREE and doesn't require any installs.