Open Adobe Photoshop and open the image file for your DVD case cover. The size for a standard DVD case is 3240 x 2175 (170 spine) pixels. The spine is not always necessary depending on how complex you want your design. The 170 pixels is the area in the middle of your design where the spine would lie. The dimensions given above are the appropriate size and resolution to fill the entire case--front, back and spine.
Make sure your printer is connected, and load the glossy paper.
Click on "File" and then "Print" in Photoshop and begin tweaking settings for the printout. Select the color you prefer, and the correct paper. Most printers give you the option of selecting the type of paper, because printers deliver ink differently depending on the paper's thickness. Click "Print" when you're ready.
Remove your printout and let it dry. Take it to a cutting surface--such as a wooden board or tile--after about 10 minutes. Use your ruler and Exacto knife to cut off the white around the edges of your new cover, so it will fit in the DVD case.