For those who don't know how to customize DevPro, here is a guide. If you have any questions, post them here.
To start customizing: Start Devpro and click at the top customize. Once there, you will have options to customize how you duel. To choose what you want to customize, there is a tab at the bottom right of the Devpro window ranging from Backgrounds to Music.
To customize your background, you will need to import an image from your computer. Depending on the size of the image you want as your background, there will be some resizing done by the Devpro program. Weather its to enlarge the image causing blur or shrinking the image so that's it's difficult to see (not that the duel field is of any help when it blocks your custom background).
To import an image, go to "backgrounds" when you click the customize tab at the top. To the left of the backgrounds tab you selected to customize, click "add" (there is a button on the left that has an add button, don't click it). Once you click add, a window will pop up showing your computers files, go to your computers images and import the image you want as your background.
Once imported, it will appear in Devpro as a background for selection. Right click on the image, and go to the option "install" and a window will open with the word "Success!" as confirmation that it installed correctly. Go to "preview" to see what it looks like - this will only work if you have a Duel Replay saved.
Customizing Card Sleeves:
To customize your card sleeves, go to the customize tab at the top. At the bottom left there is another tab, click "covers."
To customize your covers you need the correct size in order to see the "card sleeve" clearly. Unlike customizing your background, you need the correct size so that the image isn't a blurred mess. Here is a blank size sleeve for use in customizing your card cover sleeves:
Once you have the correct size and correct image you want, click the "add" button to the left of the bottom left tab that says "covers." Once you click add, a window will pop up. Go to your computers images and import the image you want. Once done, it will appear in the DevPro window next to the kaiba sleeve that is available when you installed Devpro. Right click on the image you imported, go the option "import" and a window will pop with a "Success!" message. To preview your sleeves, go to preview and load one of your duel replays to see your custom sleeves.