
If you are in the UK then your own vet tkes the X-ray and this is then sent off to the British Veterinary Association board of experts for scoring under thenBVA/KC Hip dysplasia Scheme.
It is best though to use a Vet who has a lot of experience X-raying Hips for the scoring, as the score can vary a bit if the x-rays are not just so.
The dog can be scored anytime over 12 months of age, but can only be done once, and if you appeal the score the same x-rays have to be used for any re-evaluation, so it is important to get good ones.