How to install lights behind an old window frame to display a photo.

This is nothing more than a string of LED lights (like Christmas lights) stapled on the back side of the window frame. Use wooden blocks to hold the window out from the wall so the lights won't get crushed.

LED rope lighting will do the trick. Buy them online, Walmart, etc.

This is what a fellow Hometalker member did to create a "window" at the end of a dark hallway. This should help a lot because it looks like a window where there is none.

https://www.hometalk.com/diy/windows-doors/windows/my-long-dark-hallway-needed-some-lights-14056800?expand_all_questions=1

Using Christmas lights and a staple gun, go around the edges of the window glass area. If the window has dividers, go there too. Then just hang and plug in. Easy as pie.

You could frost the glass in windows so you do not see the wall, staple lights onto the back or with clips, so can replace if needed. You can hang from ceiling in front of wall with chains or attach to wall with wood block spacers so as not to crush the lights, If you wanted to put a small valance across the top to make it look like a real window. Post pictures to show what you decided to do, thanks and Happy Holidays