Photo Merge
This trick can be used to replace part of your image or stitching images together.
Keywords: photoshop, merge, merging, stitching stitches

1. Open the first image in Photoshop.

2. Copy the second image on a second Layer.

3. Change the Layer Mode to Difference*

4. Move the top image until similar areas stop creating those nasty colors and come to black and white.

You might have to turn layers on and off to make sure you are alligning the right areas.

In many cases you will have to rotate or modify the size of your secondary image.

5. Change the Layer Mode back to Normal.

6. Erase imperfect areas using a soft edge brush.

* In some cases you might want to leave the Layer Mode to normal and drop the transparency to 50%.