I would like a check box on a selected image

I currently have a white circle to overly an image, when the image is selected. But it doesn't look good.  Instead, I would like to see the white circle replaced with a check mark, one that has a transparent background if possible.

Thanks

Please try using Image Checkboxes widget instead of Image Radio Buttons.

Here is how it looks:

Thanks AndrewHag, I played around with css and found a different solution.