Nick, this is quite a challenging ID.
I have some experience of both
tagis and
crameri in southern Spain, primarily in the Hoya de Baza, on a small number of occasions.
I would agree with David that it is not easy to confirm on the basis of just one photo - do you have any other shots of this insect?
As Roger says, it would be useful to see the underside from a 90 degree perspective.
My comments would be as follows:
As Roger mentions, the discoidal mark being fused to the costa is suggestive of
tagis,
but the discoidal mark doesn't taper away as in most examples of
tagis that I have seen, it being more like most examples of
crameri, in my limited experience.
The hindwing curvature looks very suggestive of
tagis, but the angle that the photograph was taken at makes this less than 100% conclusive.
Another distinguishing feature is the clarity and definition of the white marks on the unds hindwing, particularly how the white markings stand out from the green (black/yellow) areas. In my experience,
crameri shows a cleaner definition between these areas, with "whiter" white patches (and usually larger) distinctly separated from the "green" areas, whereas in
tagis, the definition between white and "green" areas is more blurry, less defined, and the white areas themselves are less bright and clear. In this matter, your photo is about half way between the two!
In the wild, in the Hoya de Baza, I actually found that the size of the butterflies when viewed on the wing was the most reliable indicator of ID. Portuguese Dappled White, flying in the company of Western Dappled and Green-striped, was easily identified due to its significantly smaller size. The wingspan of
tagis in this part of Spain is consistently about 2/3 the wingspan of crameri, making it very easy to differentiate.
Below are two photo's taken in the Hoya de Baza of tagis and crameri.
I would be reluctant to stake my (non-existent!) reputation on a definitive ID for your specimen, but I would go 60% crameri, 40%tagis.
Here are my shots:
tagis
crameri