hi mihai,
interesting material, 2cy get harder and harder as they fade out but i think you got a cachinnans on the left, then the bird in question and then a michahellis to the right.
now on first look the 4cy gull in the middle has this small dark looking eye and a seemingly weak bill but a closer look should be given to that crown line, with the highest point almost above the eye, iris could be paler than in this foggy look, and head and neck give a thick impression which is strange for caspian (especially in the 3rd pic!)
i'd call it a female type, they're often more difficult in structure evaluation.
pro caspian are the very dull yellowish legs, dark iris(?), extended black on bill, a largish mirror on underside of p10.
too many uncertainties on this one to come to a definite conclusion, but most things point to cachinnnans i think, with a strange head shape.
the 3cy type in the last 2 pics is a powerfull michahellis possibly with a deficiency of breeding hormones, unusually pink legs, dark eye and bill without yellow.