In case u don't have Photoshop, u can download it link

Now that u have Photoshop, we can get started.
First u need to click File--->New---> width 800, height 100 pixels. Then u click Ok and u have a background.

Now u click File--->Open and u select a foto u want to open. Then u crop and resize it. I usually choose 110 of 120 height. Now right click on little window and verplaats to new window. Now your image is in new window and u need to drag it to your banner. Then u use a little arrow from the panel on the left and verplaats your image where u want it.

You do...

PNG is a strategically cropped layer. u can use it for your icons, banners, random fan art... u can make your own PNG of download one.
link

You drag PNG files same way u do with link

Here are some PNGs, all from Deviantart:
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link

I didn't test all of these so sorry if some are not very good.