Arguably the oldest picture of a bicycle is the stained glass window dating from 1642 in a church in Stoke Poges, near Slough in Berkshire. It's genuine, and apparently shows a naked man riding (to modern eyes) a primitive velocipede, and playing a trumpet at the same time, which may be quite an interesting fantasy for someone.
For a while the world thought that Leonardo da Vinci had dreamt up the principles of the bicycle, as recorded by drawings in one of his sketchbooks that surfaced in 1974, but it's now recognised as a hoax, a modern addition. Knowing Leonardo, if it had been genuine, it would have had a naked man riding it.
But here's a new candidate for the 'world's oldest depiction of a bicycle': this mosaic on the Grand Union Canal towpath just outside Brentford. Stylistic analysis, and comparisons to the handlebar and frame designs on the Ravenna mosaics, attest to a sixth-century origin. Or perhaps an art-student project for the council last year.