Feel free to give it a go and see if you can identify these individuals. They're all adults and they all occur in North America. Answers below.
Row 1: Kumlien's (Iceland) Gull, Slaty-backed Gull, Glaucous-winged Gull.
Row 2: Ring-billed Gull, Bonaparte's Gull, Laughing Gull.
Row 3: Herring Gull, Lesser Black-backed Gull, Black-headed Gull.
Row 4: Mew Gull, California Gull, Glaucous Gull.
Row 5: Thayer's (Iceland) Gull, Western Gull, Great Black-backed Gull