Wondershare Photo Collage Studio 4.2.11.20 Online Manual

Click the “Mask” tab to add a mask to the current photo. You can select a mask type from the Mask Type drop-down list. There are six built-in mask types available: Circle, Customize, Other, Rectangle, Shadow, Theme. Select a mask type and all the masks of the selected mask type will be shown in the mask pane below. Double click a mask to apply it to the current photo. You can also select Customize to add masks of your own from your hard disc to the Customize type list.

Note: Masks can only be black and white pictures. The black parts of a mask will block your photo, and the white parts of a mask will be transparent.

If you want to clear the mask from photo, just right click the photo and choose the "clear mask" action. Also you can directly click the button   in photo edit menu to delete the mask.