To unlock The Image of Faith trophy in Assassin's Creed Odyssey you must complete the quest chain of the same name. This should appear as a blue diamond with an exclamation mark in the region of Elis. Fast travel to the Temple of Apollo in the Kingdom of Pelops in order to reach this marker to the south. Note that you will need to have installed at least update 1.11 for this quest to appear, as well as have reached Chapter 5 of the main quest. Speak to Polykleitos kneeling by the side of the road to start the arc.
The Measure of a Man
Head to the Quicksand Bay bandit camp directly south-west of the quest giver. The tools are in a pouch near the torchlit tent. Return to Polykleitos and then escort him to Linou Farm -- nothing much happens on the way.
After this first quest, the next three can be accepted in any order. All start in your immediate vicinity at Linou Farm.
Down from On High
Heriphile is nearby at the sheep pen. Once she has requested that you find her totem, head straight up the hillside to the south and inspect the wolf spoor, blood, dead sheep and basket, all of which are on the near side of the hill with the sheep at the crest. You will be directed to a nearby wolf den further south with two regular wolves and an Alpha Wolf. Collect the totem and return to Heriphile.
Menalkas is lying on the floor near a field of crops at Linou Farm. Talk to him and then investigate the immediate area -- the pots in the cart, the stacked crops by the silo, the smashed vases by the silo, the abandoned offering near the house and the Civilian in front of the house. Once you have finished you can return to Menalkas and decide whether this is a divine or earthly matter. I chose earthly, and fired the silo.
The Wild Hunt
On the western side of Linou Farm, in front of a small house, Akatos is sitting looking mopey. Go and find his daughter at a lake to the north-east (it's a Historical Location called Forest of Pholos). Myrto, your target, is on the north-western bank of the lake. You can choose to hunt with Myrto or send her home and hunt for her. I chose to hunt with her, though she doesn't move from her spot while you hunt anyway. You need to gather deer meat; luckily the lake is almost overrun with frantic male elk who are an easy target. Take just one down to fulfil the initial requirement. Talk to Myrto and then track down six more deer -- there's at least that number in the immediate vicinity of the lake. Go back to Akatos to finish the quest.
Once you have completed all three quests above, return to Priestess Hexione.
Chicken or Egg
You need to head to an unmarked farm north-east of Linou Farm, and beyond the Dryad Camp. As you approach Kallistratos, you will be attacked by murderous chickens. Yes, that's right -- they go down easy but they pack a nasty peck. Speak to the fallen man and then return to Chalkippe and the Priestess. You will immediately be taken into the next quest.
A Matter of Faith
Unfortunately the people you need to speak to aren't highlighted, but Chalkippe, Hevmonos and Heliphile are milling about outside Myrto's current location and can provide some clues. Speak to all three to get the location of a cave, a fair ride to the south-east and east of Neda Camp. Enter the cave to find Hexione. You will be directed to retrieve a plant protected by a particularly powerful Alpha Bear. Defeat it and investigate the plant and then talk to Hexione again. As with the rest of this arc you can choose to play into their divine pretensions or be more humanly assertive. I chose earthly options in all cases -- It doesn't appear to make a huge amount of difference. Return to the village and Myrto. Decide whether to present yourself as a god or a human in the final speech to the villagers.
Once you finish the final quest, the trophy will unlock.