+ If it is from a file, then it will be returned in `filename_return'.
+ filename_return may be NULL; also, NULL may be returned (e.g., if
+ it's a screenshot or video capture.) You are responsible for
+ freeing this string.
+
+ The size and position of the image is returned in `geometry_return'.
+ The image will generally have been scaled up to fit the window, but
+ if a loaded file had a different aspect ratio than the window, it
+ will have been centered, and the returned coords will describe that.
+