Object identification tries to discover what objects the computer is looking at. This involves finding characteristic features and using a database. Scene reconstruction tries to discover where the objects are relative to the camera, and what shape they are. The bottom-up approach Strongly influenced c. 1980 by David Marr . First do some image processing .
Edges are places where the image brightness changes rapidly and consistently.
Shapes are found using techniques that group edges that lie on smooth curves or straight lines. Image structures are found by grouping together shapes with similar characteristics. Then find some layout - where things are in space. Many techniques have been explored e.g. Line labelling where the geometry of different kinds of line junctions is exploited to yield a 3-D interpretation. Linear perspective where parallel lines in space are seen as a fan of lines in the image.