I had to consult a list of butterflies in Tunisia and go through several entries before I was able to visually identify the butterfly in the above photograph as the Old World Swallowtail otherwise known as the British subspecies of (Papilio machaon brittanicus).
The imago typically has yellow wings with black vein markings, and a wingspan of 65–86 millimetres (2.6–3.4 in). The hind wings of both sexes have a pair of protruding tails which give the butterfly its common name from the resemblance to the birds of the same name. Just below each tail is a red eye spot.
Papilio machaon was named by Carl Linnaeus in the 10th edition of Systema Naturae in 1758, alongside nearly 200 other species of butterfly. Later, Pierre André Latreille designated it as the type species of the genus Papilio. The specific epithet machaon refers to Machaon, son of Asclepius in the works of Homer.