Our developers have some problems with displaying images that are round or with rounded edges.
If you have a bitmap you want to round the edges of, you need a bitmap with a transparent rounded-edge center and edges the same color as the background of your channel to overlay on top of it. This will create a rounded edge image to display.
A better way is to generate rounded edge images on your website and download them to your device. You can do this using toolkits like ImageMagik or GD, which might even be installed on your web server by default.