As others have noted, they don't really go anywhere, but they are at risk of being damaged or destroyed. It works something like this-

You save a photo to your computer. Your computer saves the string of 1s and 0s in a specific location(s). So lets say it saves photo 1 to a space it calls A1 through A10 (simplified for ELI5). Two things happen- When you tell you computer you want to see the picture, it reads what is in space A1 to A10 on the drive. Also, it knows NOT to write anything else in those spaces, because if they do, it will corrupt the photo.

When you delete it, it removes it from the "table contents" , and now these 2 things happen- If you look for the file, you can't find it, because it's not in the table. Further, now any other program sees no restrictions to write to A1 to A10.

So there is a chance 1 year later you can still restore that file if the computer didn't write over any part of it, but there is also a chance that it will be corrupted because parts or all of the file have been overwritten.