SeekPixel

This should be a square logo for your resource. Accepted file types are .jpg and .png

The safe area aspect ratio is 4:1, and the total header aspect ratio is about 10:1 (width : height), although it can also be wider.

Your banner should be about 7,500 by 750 pixels, with a safe area of 3,000 by 750 pixels in the center of the banner. For the best results, use a wider image and horizontally center important content.
Accepted file types are .jpg, .png, and .gif