Here is a quick and simple way to merge those 2 images into 1 and make them look like they were made that way.
1. Start by creating a blank canvas, mine is, 361x229 (but it can be whatever you want). Open up the first image you would like to merge and paste it onto this canvas.
2. Now take the picture and select about half of it, I left out the right side out in my selection.
3. Now go to Select -> Feather, change the value to 30 px and click ok. Once that's done hit CTRL+C then CTRL+V (this will copy the selection and paste it). Then delete the original layer of your image (the one you pasted at the beginning of the tutorial).
4. Now paste the second image you want to merge into the canvas and repeat the above steps, this time leave some room on the left side for the selection. Play around with the opacity until you get the merge you want.
More Tutorials: 
