Most of the popular image editors such as Photoshop and Paint Shop Pro are commercial and paid softwares. However, there are a number of graphic editing softwares that are available for free. They are not popular as they have not be publicized themselves well and most people are still not even aware of their existence.

The examples of such softwares are:

The Gimp
It is considered to be the best free image editing software. Its features are comparable to Photoshop. However, it is not so easy to use as the commercial ones. It is mostly used on Linux as Photoshop cannot be run on it.

GIMP actually stands for GNU Image Manipulation Program. It was designed to compete with Photoshop as an open source software, just like OpenOffice.org is a competitor for Microsoft Office and Mozilla for Internet Explorer.

Gimp is still not very popular due to its unusual interface. It is based on Linux GTK system and is broken down into a number of small components. This makes it difficult to run it on Windows. One advantage of Gimp is that it lets you change its menus and sub-menus into toolbars which makes it easy to use. In fact, in some areas Gimp overpowers Photoshop, like in the number of filters in which Gimp has surely overpowered Photoshop. Its best feature is that it provides a large number of functionalities, that too for free.

Paint.NET
Paint.NET has been created recently but has become quite popular in a short span of time. It offers a very powerful image editing program based on the 'Paint' programs that is included in the Windows Operating System. It is popular as people are already familiar with it.

It has been developed at Washington University and is supported by Microsoft. Therefore, it's possible that it might be included in any new version of Windows that will be released in the coming future.

SodiPodi
It is a software that can be compared to Macromedia Freehand or Adobe Illustrator but cannot be considered as an alternative to Photoshop. It can be used to draw vector graphics or create your own artwork. It can be used to complement Gimp and Paint.NET softwares and it also allows users to apply effects and filters while making logos or other designs.

Picasa
Picasa is a tool that can be used to manage photos and make them ready to be displayed on a website. It has recently been bought by Google and made available for free download. It can also be used to apply simple effects such as the removal of the red-eye and the like.