The thought of a system that could search the photos taken by a bunch of strangers on the smartphone looking for one specific person seems scary and creepy at first. However, there is a lot of good that can be done with something like this as well. Think for instance about all the people you see shooting photos with smartphones at a theme park. Consider if a child goes missing and all of the photos being taken there might show what happened to the child to help parents or police locate the missing little one.
Rice University has a paper that details just such an image search solution called Theia. Theia would be an opt in system that would allow the user to mark a folder on their smartphones that could be searched by Theia to check their images. Then when a search is being made, the Theia search program would look at the meta data in the images including time and date to find clues about what happened.
The Theia system uses cloud computing to offload the images and perform the search rather than tying up the smartphone CPU performing the search on the user device. The team at Rice has shown that using the Theia system reduces the cost to run an image search of this type by an average of 59%. This is an interesting way to search for missing people and to try to catch crimes by looking at photos shot in a specific location at a specific time. There is a chance that some stranger caught a crime in action and didn't even know it.