Here's the inside joke about the real-life scandal that backgrounds "Picture of Innocence": Liza Goddard (who plays Marion Bell) successfully sued a national British newspaper which printed a story alleging (untruthfully) that she and John Nettles were having an affair because their characters Jim Bergerac and Philippa Vale in Bergerac (1981) were romantically linked.
It is stated that DCI Barnaby (played by John Nettles) had a brief fling with Marion Bell (played by Liza Goddard) about 30 years before the events of this episode. Curiously, Nettles played Bergerac (1981) in the drama series of the same name about 30 years previously, and one of his love interests was Philippa Vale, played by Goddard.
According to DCI Barnaby's fingerprint card, he was born on 20 Apr 1943, making him 64 years old. (John Nettles was born on 11 Oct 1943.)
According to the fingerprint report. Tom's middle name is Geoffry, an uncommon way of spelling the name (more frequently written as Geoffrey or Jeffrey). The name is an old German word meaning peace. The test seems to have been done by DCI Spelman on 06/12/2006 which would be in keeping with the bare trees.
The story revolves around traditional versus digital photography. At the (traditional) photography exhibition, most of the photographs displayed are of cats or food plates - two subjects which are usually derided as being "all one sees" on the (digital) internet.