What I see as rectangular are rectangular images within transparent ovals. So it looks like you should play with size and proportions (to get a horizontal oval, a vertical oval, a round oval
) of your image: try to allow some extra background of transparent colour (white?) to fill the oval around your rectangle of desire.
Here's an example of what I mean (notice the oval "allowance" - extra space, transparent background is some .png property - white background was converted by a handy online tool):