The latest Totally Handy Web Site is one I frequent regularly. I run a few web sites and do a lot of projects that require image editing. Sometimes I do some of the work at the power company when it is slow, or at the FD in off hours, or at home. It was problematic to use different types of software depending on where I was at and what was (or was not) installed in each place.
Introducing Pixlr (http://www.pixlr.com), a FREE full-featured image editing application that is entirely web-based. If your web browser's Adobe Flash plug-in is up to date, you're all set to go.
You can upload images from your own computer, make your edits, and re-save them to your computer. You can also designate the URL of an image online to load into Pixlr, and then save your modified version locally. And that's for anonymous users. If you choose to create a free account with them, you gain access to their "cloud", allowing you to store your images online and access them from anywhere.
To create an account, go to the editor and choose to open an image from the library. The pop-up window will ask you to log in, but there is a link just below the password field labeled "sign up for pixlr". Username, email, password, you're in, no other info required.
There are a few tutorial paths you can take if you're not familiar with image editing, and it won't be long until you can navigate the application with relative ease.
Unless you are in need of industrial strength super image editing software and just must install PhotoShop or similar stuff on your PC, Pixlr is your answer, is totally free, and accessible from anywhere you can get online.
Check out their FAQ, which addresses privacy and operational concerns. Also, here are straight links to sample tutorials for "creating an intense portrait", and working with "selective coloring". There are also a lot of video tutorials made by a variety of users that can be found on YouTube to help you through certain tasks.
Very slick. Very cool. Very totally handy.