First, you will need some type of image editing software that will let you crop an image. If you don't already have software that was included with your camera or scanner, then you can download shareware image editing software that can do the trick. You don't have to buy an expensive image editing software suite to crop and resize an image.
For this tutorial I will be using adobe photoshop to crop my image. The technical procedure will be different for each software product, so I will focus on concept only. Starting with this painting of an alien girl, I want to create a thumbnail that will be interesting. Simply reducing the size of the image to 80 pixels is not in my best interest here. Although some images are perfectly suited for a simple reduction in size, in my opinion, this one isn’t.