Round the corners of an image

The corners are cut with a clipping path rather than filled with a colour, which is the difference between an image that works anywhere and one that only works on white. A filled corner looks fine on the page you designed it for and shows as an obvious white wedge on a dark background or a coloured card. Transparency has no such problem.

That is also why the output is PNG. JPEG has no alpha channel at all, so saving a rounded image as JPEG fills the corners with a solid colour — usually black, which is worse than the white you were trying to avoid. If a service insists on JPEG, the honest answer is that you cannot have rounded corners in the file and should round them in CSS instead.

A circle needs a square source. At 50% radius a non-square image becomes a stadium shape — rounded ends on a rectangle — rather than a circle, because the radius is measured against the shorter side. Crop to 1:1 first if a circle is what you want.

Worth mentioning: for a profile picture you often do not need this at all. Almost every platform crops avatars to a circle in CSS, so uploading a plain square gets you the same result with none of the transparency handling. Rounding the file matters when the image will sit somewhere you do not control the styling — an email, a PDF, a slide.