If you are editing image, what software you use? MS Paint? Adobe Photoshop? For me, MS Paint is fast, and only fast. Nothing special. Photoshop, is not free. If you want to install, it requires a lot of space.
So, I use 2 image editors, Paint.NET and GIMP Portable. Both of them support layer editing. Very nice. Actually, I prefer using Paint.NET. Because it is more usable (easier to be used) compare to GIMP. The interface is easy to understand. However, it does not as powerful as GIMP.
GIMP can create .gif file with animation (read more). For me, it is quite difficult to be used. Besides that, if you are using GIMP Portable, several plugins are already packed with it. Therefore, there are a lot of extra features. However, because of usability problem, I can hardly to find the function I want, such as draw the vector. If compare with Paint.NET, GIMP is slower to startup.
Actually, Paint.NET installation file is smaller than GIMP. However, Paint.NET requires .NET Framework. So, you need to install .NET Framework in order to run Paint.NET.