Pixlr is an amazing photo editing program. There are three different versions that you can use. I chose to use Open Pixlr editor (Advanced) to make a black cat and a picture of Jack O'Lanterns into a spooky halloween collage with red highlights.
Before you start editing your photos you need to simply add a new layer. Click on the layer tab at the top of the menu. In the layer tab click on "Open image as layer". Once you have done this import your picture of a cat. Finally zoom in on the cat's eyes.