Put your pictures on cardboard or poster board the size of the window opening and attach to back of frame so the window becomes the frame. It's a country chic idea.
Rebecca...Yes....you can use large picture or done panes.
If it still has the glass in it.
Just attach pictures to the back of the glass panels
Just hang pictures on the inside of glass you could decorate the glass around the pictures and put the pictures in the middle of the glass you don’t need a boarder.
Pinterest or Etsy. You can paint the clear glass
Does it still have the glass? You can attach photos to the glass itself. If it does not have glass, buy small picture frames that fit inside each pane and display them that way.
How to attach?
You could tap in glazing points to hold the cardboard backing.
You could have the cardboard backing be larger than the opening and tack it in place with thumbtacks.