Interestingly the British Birds Rarities Committee commented that the award winning photo was selected because it was considered to have captured the critical features of Glaucous-winged Gull and indeed this is accurate.
However out of the large selection of photographs that were taken of this bird, this was the only photo to suggest so many critical features. If you consider the photo below, this photo captures a very different bird which suggests little in the way of Glaucous-winged Gull structural features.
The optimum way of considering photographs in the assessment of difficult rarities (especially where structure and colour tones are critical) is to look at a range of photographs at different angles and lighting. The 'true' bird should emerge as an interpretation of a balance of this range. On balance the Beddington Bird did not appear to show all the critical features and the award winning photo has captured a moment- a posture, angle, effect of black wire in back ground accentuating depth of bill, angle of photographer, distance of bird from photographer etc. For this reason indeed it is certainly an award winning photo as it very instructive and high lights the perils of interpretating too much from a single photograph in the assessment of a rarity.
More on this gull here: