Resolution and cropping rules for the favicon
A favicon will be visible to any visitor in their browser tab.
That logo should be 32x32 pixel size. The file should be a jpg, png, gif, or .ico.
If the photo you upload isn't 32x32 pixel size, it will be resized automatically, and taller images will be cut in the middle (top and bottom will be cropped).
To enjoy the best results, you should use the recommended size.
You can add a .ico file type to ensure visibility in different browsers. In particular, Microsoft Edge seems to rely on this file type, but a .ico file should work in other browsers as well.
What tool to use to resize and crop images
You can use a basic image editor (like Paint) or some online tools like Cropp.me or Cut My Pic.