Definitions are not strict and even Russian links are not consistent or definitions are rather vague.Stopkа
``a small Stakan or Rjumkа, usually 50 - 100 ml``
(Сто́пка — небольшой стакан или рюмка)
Etymology from old volume measure (Как единица объёма).
Seems related to the volume, not the form (compare with shot glass).Stakan
`` drinking vessel of cylindrical form without handle``
(Стака́н — сосуд, близкий по форме к цилиндру, без ручки).Rjumka
Usually used for strong spirits, it is small in size, has no stem.
(для употребления спиртных напитков).
A native Russian speaker can hopefully shed more light.
The image is from a Russian link described as rjumka.