1. A computer program product, encoded on a non-transitory computer-readable medium, operable to cause data processing apparatus to perform operations comprising: generating a correlation value indicating a likelihood that a face included in a test image corresponds to a face associated with a pre-determined base image; determining that a correlation threshold exceeds the correlation value and that the correlation value exceeds a non-correlation threshold; confirming that an elapsed time between the base image and the test image is below a time threshold; generating a similarity score based on one or more exposure values and one or more color distribution values corresponding to the test image and the base image; combining the similarity score with the correlation value to generate a weighted correlation value; and determining that the test image and the base image are correlated when the weighted correlation value exceeds the correlation threshold.