1. A method comprising: receiving, by one or more processors of a mobile device, a first plurality of images from a camera of the mobile device; generating, by the one or more processors, digital representations of the first plurality of images; accessing, by the one or more processors, at least one data structure stored by the mobile device, wherein the at least one data structure includes digital representations of a second plurality of images; determining, by the one or more processors, whether a degree of similarity between a digital representation of a first image in the first plurality of images and a digital representation of a first image in the second plurality of images is within a first similarity interval or a second similarity interval; responsive to the one or more processors determining that the degree of similarity between the digital representation of the first image in the first plurality of images and the digital representation of the first image in the second plurality of images is within the first similarity interval, sending, by the one or more processors and to a remote server, a message that indicates the first image in the first plurality of images corresponds to the first image in the second plurality of images; determining, by the one or more processors, whether a degree of similarity between a digital representation of a second image in the first plurality of images and a digital representation of a second image in the second plurality of images is within the first similarity interval or the second similarity interval; responsive to the one or more processors determining that the degree of similarity between the digital representation of the second image in the first plurality of images and the digital representation of the second image in the second plurality of images is within the second similarity interval, sending, by the one or more processors and to the remote server, a message comprising data that represents at least part of the digital representation of the second image in the first plurality of images; determining, by the one or more processors, whether a degree of similarity between a digital representation of a third image in the first plurality of images and a digital representation of a third image in the second plurality of images is within the first similarity interval or the second similarity interval; and responsive to the one or more processors determining that the degree of similarity between the digital representation of the third image in the first plurality of images and the digital representation of the third image in the second plurality of images is not within the first similarity interval or the second similarity interval, refraining, by the one or more processors, from sending a message associated with the digital representation of the third image in the first plurality of images to the remote server.