How to Change Your Minecraft Main Menu Background with Custom Background HD
Finding and Preparing Your Image
Start with any PNG image you want as your menu background. Screenshots from your own world work well, but so do wallpapers or artwork you have permission to use. The pack supports HD images, so a high-resolution file will look sharper than a small one. Keep in mind the menu overlays text and buttons on top of the image, so busy or very bright images can make the menu hard to read. A darker or simpler image usually works best.
Replacing the Background File
Open the Custom Background HD resource pack as a zip archive using an archive tool. Navigate to assets / minecraft / textures / gui / title / background. Inside you will find panorama_overlay.png. Rename your chosen image to exactly panorama_overlay.png and drag it into this folder, confirming that you want to overwrite the existing file. Save the zip. Now apply the resource pack in-game through Options, then Resource Packs, and move it to the selected side. Return to the main menu and your new background should appear immediately. If it does not, make sure the pack is actually enabled and that your image kept the correct filename and PNG format.