The potential of surveillance practices to undermine the presumption of innocence is a growing concern amongst critics of surveillance. This paper attempts to assess the impact of surveillance on the presumption of innocence. It defends an account of the presumption of innocence as a protection against wrongful criminalisation against alternatives, and considers both the ways in which surveillance might undermine that protection and the—hitherto overlooked—ways in which it might promote it. It draws on empirical work on the causes of erroneous convictions to suggest that surveillance can be used in ways that prevent innocent people being erroneously charged and convicted with crimes, by providing a source of exculpatory evidence for use in police investigations. It is argued that surveillance practices do not necessarily undermine the presumption of innocence but can be reformed in ways that both reduce the risk that they will cause wrongful criminalisation and increase their power to protect those already under suspicion.