Image Resizer for Windows is easy to use and powerful software. It is very small in size (901 kb) & absolutely FREE.
Further, you can use it for a single image resize, or resize multiple images in few seconds directly from your windows explorer.
This software support most of the common image formats i.e. JPG, JPEG, PNG, BMP, GIF, ICO, TIF, TIFF WDP, etc.
The only thing which requires to make it work is .NET Framework 3.0/4.5 or later on your machine.