Lepidea sinapis/juvernica complex
The two species Leptidea sinapis and Leptidea juvernica are very similar; reliable external features that could facilitate photo identification, have not yet been found.
The species Leptidea juvernica has been certified in Greece (only in Rodopi) after the work: SHTINKOV NIKOLAY, ZDRAVKO KOLEV, ROGER VILA AND VLAD DINCA: The sibling species Leptidea juvernica and L. sinapis (Lepidoptera, Peninsula) in the Balkan: genetic structure, and morphological variation. www.elsevier.com/locate/zool Zoology 119 (2016) 11–20
There is also the possibility of an online test for identification: see in CUVELIER S. & MAERTENS D .: Trial test of external morphology-based identification of Leptidea sinapis, L. reali and L. juvernica (Lepidoptera: Pieridae) provides opportunity for an online identification platform. Phegea 45(2): 41–45.
Here are twenty-four photos of Leptidea butterflies, most likely Leptidea sinapis (from the Rhodope where Leptidea juvernica has also been confirmed).