GIMP (GNU Image Manipulation Program) is a free software which you can easily download from the above link. GIMP can be used for quality image editing and retouching. If you are looking for a free Photoshop alternative, then GIMP is a great option worth trying. Initially, GIMP was created to run on UNIX based operating systems such as Linux, but later GIMP was ported to other operating systems including Microsoft Windows and Mac.
Designed by a dedicated team for graphical user interface, GIMP has an easy to use interface. The default user interface has tools on the left side and dialogue on the right side. GIMP Toolbox contains the tools for image editing needs. GIMP lets you select color in many ways. The Blend Tool lets you blend colors. Pencil, Paint Brush, eraser, and other tools can be used to draw and edit pixels of an image.
There are some tools for editing large portions of an image such as Bucket Fill and Blend Tool. The blur and the sharpen tools can be used to improve photographs. Similar to Photoshop, GIMP also uses layers to help in image editing. For example, if you want to write some text on a photo, you can create a text layer using the text tool.
By default, GIMP has a large number of filters to produce effects such as Drop Shadow, Blur, Gaussian Blur, etc. New features can be added to GIMP using contributed plugins. GIMP supports all popular image format and file types such as JPEG, PNG, BMP, TIFF, GIMP, PSD, SVG, etc. You can use it to convert from one image format to another.