In general you will only get a point the first time you visit a grid square, and your photo is moderated as a "geograph". You may also get extra points if you are one of the first 4 people to visit the square. Subsequent photos in the same square will not get you any points, photos classified as "supplemental" will not get you any points.
(From 11 May 2016 the Supplemental Classification is replaced by Image Type Tags:
see http://www.geograph.org.uk/article/Image-Type-Tags ).
Tpoints work slightly differently to the above: you get a Tpoint if you submit a geograph which has a time difference of 5 years (before or after) compared to other geographs in the grid square: So with Tpoints it may be possible to get subsequent points for the same grid square.