For large but not gargantuan images, create a link to a larger version of the image. Using the image itself as a link is a good standard.
For very large images, such as extensive scrolls, antique maps or manuscripts, or wide-field astronomy, use Mirador for deep zooming.
To allow students to comment on the image and view one another’s comments, use the Annotation tool. Mirador’s deep-zoom functionality is built in here as well.