So you want a MC background for your Laptop/Computer well i found a great site that you can make exactly that!
its a little complicated though so i will go through step by step.

First go to this link: https://minecraft.novaskin.me/wallpapers

Next, scroll down until you find images with a Steve skin on it.

Then, you will want to find the picture that you would like, then left-click it.

After that, select the Steve head a tab will pop up, it will look like this:



Then, choose a skin that you would like, if you want to upload a skin from your PC, then click the upload button to the left of the
"search/player" area

if you want to use someone else's skin, then you type it in in the "search/Player" then DON'T CLICK THE SEARCH BUTTON (it doesn't work) instead click the player button.

After you are done with that and everything is looking good, then you will NOT want to click where it says "download wallpaper"

instead, click the size that you want THEN it will ask you if you want .png or .jpg
choose whichever one you want, THEN click download


AND THERE YOU HAVE IT, A CUSTOM-MADE MINECRAFT WALLPAPAER :D