The pictures Howie looks at in the darkroom.
You can get a bit of info by looking at the movie but all you need to know about them is described in the book! It starts describing them on page 129. I’ve transcribed the quotes and commented on them below that.
Brown says 13 extras were used to make these pics. You can also see Robin Hardy and some other recognizable faces in these shots. These were shot on October 21, probably at Anwoth, as were the Harvest Festival photographs.
"He selected one labelled 'Divination' and opened it. Inside was a number of photographs in folders. The first was labelled 'The Blade Bone of the Black Pig (Slinneineachd)' and contained a photograph of a crowd of islanders standing in a circle round Lord Summerisle, who was minutely scrutinizing the bone of an animal.”
Omen Stones (Col Coetn)
“The second was labelled 'Omen Stones (Col Coetn*)’ and showed half a dozen people throwing white round stones into the embers of a fire.”
The Seer in the Bull (Taghairm)
"The third was labeled 'The Seer in the Bull (Taghairm)' and had a colourful picture of a man wrapped in the hide of a bull being rocked by others on the bank of a pool.” (or the bank of river in the Ingrid Pitt script.)
The Elucidator (Peithyrnen)
"The fourth was labelled 'The Elucidator (Peithyrnen)' and contained a number of photographs that showed Lord Summerisle manipulating a machine consisting of several staves on which judicial maxims had been cut. (When turned the staves apparently spelled out messages of three or four lines.)”
We don’t see this picture nor can I find anything on the net about Peithyrnen other than in the book.
The Living and the Dead Graves
"The fifth was labelled 'The Living and the Dead Graves' and showed a woman wrapped in a blanket and lying on the ground between two holes. One had a sign by it reading 'Living Grave'; the other read 'Dead Grave.' A small circle of people looked on with concern."
So, comparing the book to what we see in the movie, I'd say we get to see pics 1, 2, 3 and 5.