To extend the background of an image with a solid background in Photoshop, all you need to do is hit Alt-Control-C and change the Weight to. Open the photo in Photoshop, and use the rectangular marquee to highlight the part of the image you want the rest of your background to match. What you want to.
 
 

How to enlarge background image in photoshop.How To Change Background in Photoshop

 
Once you’re happy with your selection, go to the Output Settings in the right-hand panel.