Geodesign Hub uses Gravatar system for profile image.
When you sign in with an email, if this email address has a Gravatar profile, the site will get that image. If you do not have a Gravatar account, an automatic image based on your email address is created. This is the image that is associated with your profile.
Go to www.gravatar.com, create a new profile with the same email address as the one you have on Geodesign Hub, and upload a photo. The photo will be automatically synchronised with your profile on Geodesign Hub.