The first pictures surrounding the portal gun representsrepresent the events in Portal, such as the reactivation of GLaDOS, the flooding of the facility with neurotoxin, and Chell killing GLaDOS.
The pictures with the cat represent the Schrödinger’s Cat experiment, which says that the cat left in a box will be both dead and alive until opened. This is talked about when Ratman puts Chell into an indefinite sleep where she would be both alive and dead until someone opens the chamber.
Finally, the last pictures are the graph shown on Chell's record, showing that she has amazing tenacity she she would never give up. This was why Ratman chose her, as Chell would be the one to actually challenge GLaDOS. The quote, "The bell invites, hear the turret, for it is knell. That summons to heaven or to hell," is a quote from MacBeth.
Also, for those of you who don't know who Ratman is, he is a surviving scientist from GLaDOS' attack as he predicted that she would kill everyone. He has schizophrenia, causing him to scribble on the walls in such a vivid pattern.