(work in progress, help will be greatly appriciated)
about
“beep boop” is a very common and a rather popular catchphrase that depicts noises and expressions of various mechanical beings, mainly, robots.
origin
(work in progress)
The catchphrase seems to used for a very long time, it is possible that it first became widly used in pop-culture after the Cinematic – StarWars: A New Hope. in which one of the secondary character was R2-D2: 
an egg shaped three legged droid that, although was intelligent, could only issue beeping sounds that could only be understood by other robots. the character was very well loved and appricated especially for his signature beepings.
Recently, the phrase recieved an increase in popularity thanks to Valve adding a new robot costume to their multiplayer FPS– Team fortress 2, the character wearin the costume – The Soldier would often utter “beep boop” in an intetionally overacted manner.
example: http://www.youtube.com/watch?v=WHvt0VBWol0
usage
The phrase is commonly used with image macros that has robots and mechanical intruments in them, as well as in images of ordinary objects, humorously depicting them as robots.
It is also used to give an impression of a robot or to playfully pretend that one is a robotic entetity
example images:
