Green’s Dictionary of Slang

Her Majesty’s pictures n.

money.

1641		Brothers of the Blade 3: Corp. I have not seene the Kings picture in silver of my owne, never since his Majesty [...] went into Scotland.
1694		Motteux [trans] Pantagruel bk V 234: [They] will think more than once how they may get good store of the King's Pictures into their Clutches.
1699		N. Ward London Spy XIII 322: We [...] Rewarded the Warder with one of Her Majesties Pictures in Silver.
1699		B.E. New Dict. of Canting Crew n.p.: King’s Pictures, c. Money.
1895		C. Crowe Aus. Sl. Dict. 63: King’s or Queen’s Pictures, money.