This is not finding people, is massively tracking people, without a jury order. Is a fishing trip.
Policemen do not need this apps. There are several police agents in each village, the 95% of the territory could be covered in a weekend just paying a visit to the five local hotels in the city, all at the same time. For bigger cities it would just take more time but is not an unfeasible task. Secret police could just book as travelling salesmen in any place of interest and silently comb the place for hours registering each crack in the tiles and each stain in the wooden floor.
As most hotels buy in mass furniture, pictures and machines, a combination of common objects will appear in all rooms. To make a database covering the 98% of hotels opened to public would not take more than two years probably, specially if they forget about pictures on the wall and focuse in rarely changing furniture or machines. To cross the database with vendors of some air conditioner model is not an unreachable goal. To estimate the area max of a room (or the size of a bed) in a photo showing a crime, can be done as long as you have enough pictures in the video. Tiles came in standard sizes. Maybe even a IA machine could be developped to search for a crack with the form of a particular broken polyline in the filtered results. Maybe police has it yet since 10 years ago... I don't know.
And there is facebook also to achieve a finer grain definition in particular areas.
Therefore the only thing new that the app adds to the equation is "you". You and the aspect of your room when you were using it.
The app is just an excuse to lure people into agreeing to be tracked, (maybe hoping that they forget about it later?). Moreover, to be tracked unnecessarily (it would only take a further visit to the place of interest to confirm the info, as I said. Policemen visit hotels in their area routinely).
But this info and agreeing can bite hard later the user in many unpredictable ways of course. For users is a "loser" situation.