Quick Picture Tools /  Rounded Corners Updated in Jan. 2020  (The old version is here.)
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Rounded Corners

Online tool to round the corners of your picture.

If width/height of the loaded image is larger than 8,000 px, it will be shrunk to 8,000 px.

You can save settings. Your settings will be saved in a browser cookie.

The loaded image will not be sent to the server. The modified image will be generated on the your computer side.

Click "Generate image" button to download your edited image.

The default download location of most of browser is "Downloads" folder.
You can change the default download location.
You can also set the browser to ask where to save the file before each downloading.
See details

Example
Rounded Corners

Free online tool to round the corners of your picture
Rounded Corners