Those incarcerated following sentencing, regardless of whether the actions of the system that precipitated such an event were in any way just, should be referred to as convicts.
As a person of conviction myself, I find this a far more empowering term than the others offered. The term "convict" indicates a powerful individual identity capable of transcending captivity, rather than a powerless pawn at the mercy of of underpaid government employees for a considerable (or indeterminate) length of time.
In my experience, the most common way incarcerated individuals reinforce their individuality and collective experience, is by wryly choosing to refer to one another as a convict... out of mutual admiration, respect, and humor.