A forest with a house in it.

No, we don't think this is the most appropriate title. The house is in the foreground of the picture (towards the bottom of the picture and in the middle) and so counts as the most salient thing in the picture. But in the noun phrase 'a forest with a house in it', the most salient word is 'forest' - it is the headword (main word) of the title noun phrase ('with a house in it' postmodifies 'forest' and so makes it clear which forest is being referred to). So the picture foregrounds the house, but the noun phrase 'a forest with a house in it' foregrounds 'forest'.

[If any budding artist wants to draw a picture of a forest with a house in it and post it up in the Language and Style Chat Room, we could add it to this explanation, to make it clearer!]

A house in a forest

Yes, we think that this is the title that is most appropriate. This is because (a) in the picture, the house is in the foreground of the picture (towards the bottom of the picture and in the middle) and so counts as the most salient thing in the picture, and (b) 'house' is the most salient word in the noun phrase title 'A house in a forest' (it is the headword [main word] of the noun phrase - 'in a forest' postmodifies 'house' and makes it clear which house is being referred to). So the foregounding in the picture and the title relate to the same thing.

[If any budding artist wants to draw a picture of a forest with a house in it and post it up in the Language and Style Chat Room, we could add it to this explanation, to make it clearer!]

Next: Foregrounding - Task B