Learn how to add a new background to an image using Gimp. 1 Open the original image and the new background in Gimp. 2 Open the layers dialog and then click on add an alpha channel. 3 On the original image choose 'Select by color' from the menu and then hit delete. 4 Copy the image. 5 On the new background, select 'Add a layer'. 6 Paste on the new background. 7 Save and you are ready to go.