In search for the biggest wasp in the world, I stumbled across the Tarantula Hawks (Pepsis heros), which often are considered to be the world's largest wasps with body length of up to 7 cm and wingspan of 11 cm. There are some more species in the same genus Pepsis (for example Pepsis apicata) with similar dimensions and nearly indistinguishable shape and colour. Also the sting is among the most painful of any insect. Actually on the picture is suggested to be the smaller Pepsis toppini, but is very difficult to be sure even for a specialist.
Source: Paul Nylander, Bugman (Collection of pictures, curious facts and topics of personal interest)