That image is 1465 x 1080 unfortunately, so will need to be downsized to be used as an avatar (the max is 100 x 100). You can do this using a free ap like Image Size, which is free.
Simon, the Christmas avatar .jpg file I'm using at present is 1586 x 1600 px. The previous one I used for several years was 3000 x 2250, both confirmed after saving the avatar itself. Am I breaking forum rules

I ask because clearly the forum software accepts these unedited sizes giving rise to my comments above.