Here is a guide on how to find the hidden mommy milkers demon picture in Hedon Bloodrite.
Finding the picture
Play the level through as normal until you pass by a room full of boxes.
Kill all the enemies, then jump up and over the stack of boxes until you find a door behind them.
Go inside, then through another door until you come upon a row of shelves. Interact with this one:
The shelf will lower, revealing a hidden room full of alcohol!
We aren’t done just yet. Interact with this shelf:
This shelf will lower as well and on the floor you will find what you have been looking for.