It would be great to be able to add the possibility to restrict tags to image regions in addition to tagging the entire image. That's very useful for tagging persons or objects.

These regions could be highlighted when the corresponding tag is selected or hovered.

For what my opinion is worth concerning extending the sqlite database, we could imagine adding a column in the 'photo_tags' table specifying the region. This region could be for instance: a rectangle, a circle or a polygon. It could be coded in some way that recalls HTML maps, like "rect(12,152,104,257)".

Consequent tools will have to be added, like a region tagging tool. 

Thanks for your consideration!