Adobe Photoshop - Paid
This is the most popular software on the market. It's perfect for storing customizable graphic information.
Gimp - Free
It’s a free program used to edit bitmap images. It’s an alternative to a paid software, although it is more limited.
Painter - Paid
Not as popular as Photoshop, but it’s still a powerful software for creating raster images.
PicMonkey – Free - Online
This online image editor includes dozens of tools, filters and effects that can be used to correct, improve, decorate and customize your images.
Krita - Free
This program similar features to Photoshop, but it's more focused on drawing.
Picadilo – Free - Online
This website offers two tools: a reasonably complete image editor and a very simple tool that allows you to create collages.