I added a photo to a page with the following method (actually to a Product in the ecommerce module to be more precise):

static $has_one = array(
'Photo' => 'Image'
);

and

function getCMSFields($cms) {
$fields->addFieldToTab("Root.Content.Images", new ImageField('Photo'));
return $fields;
}

I have photos in an asset folder. I can only associate each of these photos to only one page, as soon as the photo is used, it becomes unavailable for selection to other pages.

Could someone please help? I suspect it's a one to many type relationship I need to develop, but I am lost at this stage.

I have a solution.

In ecommerce, Product_Image seems to only attach file to an image, by that I mean that if I add a file from a From the File Store, I can only select one image per specific product.

Changing to this in Product php:
public static $has_one = array(
'MyImage' => 'Image',
);

instead of:

public static $has_one = array(
'MyImage' => 'Product_Image',
);

solved my issue.