It's still under test, but with the updated online server, you can now have:
http://www.plantuml.com/plantuml/png/0/SyfFKj2rKt3CoKnELR1Io4ZDoSatvCfBBIz8J4_bSi8YQmG0
http://www.plantuml.com/plantuml/png/1/SyfFKj2rKt3CoKnELR1Io4ZDoSatvCfBBIz8J4_bSi8YQmG0
The number just after the /png/ gives access to the Nth image.
Tell us if you find any issue! Thanks!