1. Open the image you want with rounded edges. Click for screenshot
2. Select >> All
3. Edit >> Copy
4. File >> New >> OK
5. Click the letter "U" on your keyboard to activate the Custom Shape Tool.

6. Click the "Shape" drop down arrow. Select the rounded square. Click here for screenshot.
7. Draw the rectangle from the top left corner. Drag mouse to the bottom right corner. Click here for screenshot.
8. In the shape window, go to Layer>>New>>Layer>>OK
9. Now go to the Layers control panel found at the bottom right. Click this to see what it is.
10. Put your mouse between Layer 1 and Shape 1 and click ALT until you see two black circles, one on top of the other. If you don't see it immediately, try moving your mouse slightly.
11. Should look like this
12. Go to your shape image window. Edit >> Paste.

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