‪Many studies show that teachers spontaneously and regularly evaluate what they see while observing videos of other people's teaching, but this evaluative activity has never been properly studied. We analysed how six trainee teachers went about this using resituating interviews supported by digital traces. The findings show that they evaluate using four criteria: efficiency (educational potential), sustainability (self-economy), acceptability (professional ethics) and accessibility (perceived possibility, or not, of adopting/adapting the actions identified). We discuss their implications for training.‪