CardExchange makes it very easy to add rounded corners to photos, or borders around images etc.
Under the Configuration Tab, Select Card Designer
Next we want to right click, on the field we're adding the rounded corners to. In the example below it is the photo field.
Select 'Show Properties Window'
Now, on the right hand side you will see the ' Properties' box. Select the 'Border' Tab. And you will see the option for Corner Radius.
Adjust the Corner Radius as desired. Be mindful that the measurements are in Inches. So even 0.2 of a radius is considerable. As per below image.
Once you are happy with the result. Click on the File icon, then Save. And you can now exit back to the main view.