1. Open Image in photoshop
2. Duplicate Layer
3. Make Rounded with rounded tools (see the red elips in the picture). Don.t worry about the colour. It's not the final result.
4. Just Press CTRL + ENTER then CTRL + SHIFT + I (dont forget to see the layer condition in right side)
5. Adjust visible layer and delete. (confuse..? see the layer condition in right side)
6. Adjust visible layer and Save
7. Save as PNG if you want it transparant in web page. Usually Rounded Image using in webpage.