How can I resize an image?

There are so many ways to resize an image but all of these require a tool for image resizing. The commonly or known tool for image resizing are those graphic editing software like Adobe Photoshop. Adobe Photoshop is expensive software or imaging tool but as an alternative to Photoshop, you can use the GIMP which is under the General Public License. You can use also some specialize free tools like XNView to resize an image. XNView is free software which its primary function for image viewing. But is this the best to for image resizing especially when resizing image in bulk or batch processing.