Could one image be linked to two verses?
In other words could one image lead to two different casques.

Unlikely, but it seems that some are transitional. They seem to borrow things from one another.

Image 3 shows two keys, one dangling from each arm, I wondered if this might be a clue that this image leads to two keys

“Fairy secrets come in twos….”
Usually, it’s assumed that line means that there’s 1 image and 1 verse for each of the twelve puzzles….you need both to solve each particular puzzle. 12 puzzles….12 image and verse pairings.
But….I dunno. I’ve also seen speculation that some verse lines are referring to two different things at the same time..speculation that some images/puzzles cover more than one immigration reference….etc.
(Personally, imho, I doubt that 1 image can lead to two casques. Or, 1 verse to two casques. 1 verse paired with 1 image, per puzzle. Show us how image 5 believably leads to any place other than Chicago and you might be on to something….)

A little digging into historical context of an area or persons might also be the intention of that verb.

MrSeabass

No.

“…And so the Fair Folk come to you
With their challenge and a pact:
To match twelve verses
With the sight
Of paintings twelve in colorlight.
A pair will lead you to a casque
A little digging is the task…”
Don’t know about the “little digging” though.

Unknown

Unknown:
A little digging into historical context of an area or persons

Excellent point E. The operative word being “little”.