There are quite a few orange butterflies in Europe, although different in size, with very similar black markings:
- High Brown Fritillary (Argynnis adippe), 
- Silver-washed Fritillary (Argynnis paphia),
- Cardinal (Argynnis pandora),
- Niobe Fritillary (Argynnis niobe),
- Dark Green Fritillary (Speyeria aglaja),
- Weaver`s Fritillary (Boloria dia), 
- Small Pearl-bordered Fritillary (Boloria selene),
- Marbled Fritillary (Brenthis daphne),
- Lesser Marbled Fritillary (Brenthis ino),
- Queen of Spain Fritillary (Issoria lathonia), 
- Knapweed Fritillary (Melitaea phoebe),
- Heath Fritillary (Melitaea athalia),
- Southern Heath Fritillary (Melitaea celadussa),
- Spotted Fritillary (Melitaea didyma), and
- Glanville Fritillary (Melitaea cinxia).

The best way to distinguish them from each other is by looking at the underside of the hindwings.
Most of them have small white spots or other distinguised markings on the underside of the hindwings.

The Lesser Spotted Fritillary (Melitaea trivia) looks very similar to the Spotted Fritillary (Melitaea didyma). 
The presence or absence of orange markings on the abdomen is a useful distinguishing feature, with Melitaea didyma having orange and Melitaea trivia lacking it.
On the underside of the hindwings, in Melitaea trivia the orange spots are directly against the black crescents, while in Melitaea didyma there is (white) space in between.

Psili Ammos, Samos, Greece, 3 May 2025