According to this stock photo site, the item is "Votiv relief to the god Mithras. From Vienna. Marble, 23 x 24 x 3,5 cm Inv. 8747".
CIMRM entry
1650.
White marble relief (H. 0.23 Br. 0.24 D. 0.048), found in the Botanical Gardens
in 1950. The Mithras-cult therefore must have been spread among the civilian
population. Now Vienna (Wien), Historisches Museum, Abt. für Ur- und Frühgeschichte.
A. Neumann, Ein Mithrasrelief aus Wien in Amtsblatt der Statt Wien 57,1952
(No. 95), 1f and fig.; A. Neumann, Die Fortschritte der Vindobonaforschung 1948 bis 1954 in Carinthia I, 146, 1956,463 and fig. 12; A. Neumann, Ausgrabungen u. Funde im Wiener Stadtgebiet 1950, Wien 1955,31 and pl. XXXI. See fig. 418 procured with courtesy of Dr. A. Neumann.
Mithras tauroktonus with serpent and dog. Cautes (r) and Cautopates (l), crosslegged.
On either side of Mithras' head the busts of Sol and Luna. Behind Sol
Mithras taurophorus to the right and underneath it Mithras bull-riding; behind
Luna Mithras being born from the rock with upraised hands. The border of the
grotto is decorated with seven altars in a row.
Below the central scene, 1. to r.:
1) Sol kneeling before Mithras who lays his r.h. upon Sol's head. Above Sol the protome of a lion.
2) Mithras and Sol at the sacred repast in an arched niche.
3) Mithras ascending Sol's chariot. The upper part of Sol's body and the horses
are lost.