GlassFrog currently has two ways to add an image to your profile.
Option 1: If you have not linked your GlassFrog account to your Google account, then you will need to upload a picture of your own. Navigate to your profile page by clicking on your username and selecting Settings in the scroll down menu. You can then Browse to choose the file you want to load. Don't forget to Update once you've chosen your profile picture.
Option 2: Link your GlassFrog account to your Gmail account on the sign in screen by lclicking on Sign in with Google. This will signal GlassFrog to being using your Google+ profile image.
Note: This may require you to sign out by clicking "Sign out" on the top right menu. Sign in page: https://app.glassfrog.com/session/new