[In] Photoshop how do I paste an image onto a computer screen?

[xxxxxxxxxxxxxxxx]

Step by step:
1. Have your picture on a separate layer.
2. hit Ctl + T for free transform
3. resize it so that its left border fits the left border of the computer screen
4. Click Right Mouse button and choose "perspective"
5. drag the right border until it fits the right border of the computer screen

Done!