For my holiday planning, I've been trying to perform what I thought was a simple task, but which turned out to be more complicated than I'd thought.

For a given geographical location, defined either as a place-of-interest or as a delineated area on the map, I would like to find user-submitted pictures whose tag matches a certain keyword. For instance, I'd like to find pictures tagged by users with the word 'rainbow', and whose location is within a certain location that I can define within an online mapping system such as Google Maps.

Flickr and Panoramio used to be able to allow searching by keyword (picture tag), and one could then simply zoom in to the desired location in order to be left only with relevant results. However, Panoramio is of course now offline, and Flickr seems to have dropped this feature.

What I currently do is to zoom in on the desired area with Google Maps, then bring up the Photos layer from the bottom of the screen. The downsides are of course that I have to go through pictures manually, since there is no search function for them; and that I am limited to rectangular regions of interest as opposed to being able to define a polygonal area, which you would need in order to delimit, say, the valley of a river, or the outline of a national park.

Any tips from GPS/geolocation/GoogleMapsAPI enthusiasts would be much appreciated!