runnerdud - What you are asking is pretty clear. Here is one method in Photoshop. Take a picture of the shirt and save it. Take a scan of the design and save it. Open the picture of the shirt in Photoshop. Open the picture of the design in Photoshop. Use the 'move tool' (the little arrow with the cross beside it on your toolbar) to click and drag your design across onto the t shirt window.
Use 'Edit/Transform' to adjust the size of your design. Use the magic wand to select any background and then delete it. Flatten the image with 'layer/flatten image' and save it as eg 'white skull shirt 1'. Bruce.
Use 'Edit/Transform' to adjust the size of your design. Use the magic wand to select any background and then delete it. Flatten the image with 'layer/flatten image' and save it as eg 'white skull shirt 1'. Bruce.