1. Open Gimp and copy and find the pictures you want to use (we're going to just use 2, but you can use as many as you want). I am using this and this.

2. Paste in the first image and click on the new layer button once. This will make your floating layer (the image you pasted in) a real layer. Paste in the next and click on the layer button. Use the move tool to position the images how you want.

3. Click on the rectangle select tool, check feather edges, and change the radius to around 30. Select the part of the top image you want to delete and press delete on your keyboard.

4. You can see that the blending is pretty blocky looking, so grab a big soft eraser brush and erase parts at the top and bottom (you can take circle fuzzy (19) and change the scale to 10 or so). Go to layer- merge down.

5. This part is optional, but if you want your pictures to look better blended, you can change the colors. First go to colors- brightness/contrast and change each to 5. Then go to colors- levels and change the settings to 25, 1.3, and 245. Then go to colors- curves and change the settings very slightly, depending on what colors need to be blended (I moved the curve up a tiny bit for blue and red since those are the colors that need to be blended). This whole step only makes a little difference, but it helps even out the colors and lighting. You can also use the smudge too, as I did, to blend it even more.

Here is the finished blend: