For simple photo editing, photoshop is overkill.. Here's a free alternative..
Paint.NET is a freeware editor with all the essential functions of photoshop. Normally you would never touch those advanced features offered in Photoshop anyway. What's different from other typical free photo editing software is it supports layers and history.
Everyone should download this to replace 'Microsoft Paint' which is currently in your PC =)
End Note:
Another worthy mention is Pixlr, which runs directly on your web browser so you saved the installation steps :) Just remember to save your work before you close your web browser if not it's gone forever.
I also tried GIMP which claims to be the best photoshop alternative, however it runs very slow on my PC and is eating all the resources. On the other hand Paint.NET runs very fast and doesn't impact the performance of my PC at all.