One of the most exciting projects you can tackle in image editing software that supports layering—Adobe Photoshop, Photoshop Elements, Pixelmator, etc.—is to combine images in interesting ways.
It’s fairly easy to blend two images in GIMP. All you have to do is: Open the two Images in GIMP. Blend the images using layer opacity/blend mode/layer mask. Export the resultant image as JPEG/PNG.