That picture is an odd anachronism. The figure wields something like an early 15th century gun (which to be fair saw use later), but wears something like late 16th century armour. I say 'something like' because all the details are slightly off. Combine that with the nature and style of the print (an engraving with very fine hatching), and I think it is fair to say this is a Victorian illustration, not a medieval or early modern original.

I have never seen contemporary illustrations of armoured, mounted Gunners. Mounted troops with firearms really get their start with the invention of the wheel lock and the pistol in the 16th century.