Before video call, click on ‘Choose background effect’ in the bottom, right-hand corner of your video preview. In the pop-up hit the ‘Add image’ rectangle. Navigate to where the PNG or JPEG you want to use is located on your computer. Select the file you wish to use and hit open. You can now close the window and join the call!
If you want to change your background during an active call, press the ‘More’ button in the bottom right of the Skype window and click ‘Choose Background Effect’. This will also bring you to the pop up where you can hit the ‘Add image’ rectangle. Once you select the file, you can close the window to return to your call.