Use a picture frame. One of the simplest methods for filling in a border is to purchase a frame from a local store. Purchasing some arts supplies and decorating the frame yourself is a great family project.
Download free border images from a website like myframecity.com for your photo-editing program. Open your photos in the photo editing program and open your selected frame in the same window. Use the cursor to re-size the frame and adjust it over the edge of your photo or document. Save or print the completed image.
Purchase wallpaper borders from a home decorating store if you want to fill in the borders of a room. These wallpaper borders are self-adhesive. Simply peel off the back and apply the border to the top or bottom edges of your room.
Paint the borders. Use masking tape to mark out a straight line around the border you wish to paint. You may need to use a ruler or laser guide to ensure that the tape is straight. Paint the areas above the masking tape, taking care not to paint below it. Remove the masking tape. Use a smaller paintbrush to fill in the area beneath the masking tape.
Use frosting to decorate the border of your cake. Put the frosting in a frosting bag and carefully squeeze the bag to apply frosting to the border of your cake. For a more detailed pattern, use a special tip, such as a star tip, with your frosting bag.