Engraving
Attributed to Johannes Wierix, 1572. 

Transcription of Inscription [Lampsonius]:

IOANNES AB EYCK, PICTOR.
Ille ego, qui laetos oleo de semine lini
Expresso docui princeps miscere colores,
Huberto cum fratre novum stupuere repertum,
Atque ipsi ignotum quondam fortassis Apelli,
Florentes opibus Brugae mox nostra per omnem
Diffundi late probitas non abnuit orbem.

Translation of Inscription [Lampsonius]:

Jan van Eyck, painter
I am he who ¹ first taught to mix joyful colours from the pressed oily seed of flax, ² with my brother Hubert.  Bruges, flourishing with wealth, was astounded by this new discovery, perhaps unknown in the past to Apelles himself.  Soon afterwards our uprightness ³ did not refuse to be spread widely through the whole world.

1. “ille ego qui” – For the ultimate source of this phrase, see the apocryphal opening lines to the Aeneid, “ille ego qui quondam gracili modulatus avena…”
2. “oleo de semine lini”: the same expression in the poem for Cornelis Engebrechtsz.
3. This for “probitas”.  It is hard to see quite what the author means, but “probitas” to my knowledge always has a moral sense.