According to an essay by Caroline Frances Eleanor Spurgeon called "Shakespeare's Iterative Imagery," iterative imagery, when applied to Shakespeare, is imagery that is found repeated in his various different works. Hence, iterative imagery is imagery that has various iterations, or repetitions, in Shakespeare's works. (iteration: a repetition. Origin: 1425–75; late Middle English < Latin iterātiōn-, stem of iterātiō. Random House Dictionary)
For example, in Julius Caesar, Act I, scene i, Caesar speaks of a "holy chase,"
The barren, touched in this holy chase,
Shake off their sterile curse.
The imagery here revolves around the word "holy." This imagery is similarly used in, for example, Romeo and Juliet when Romeo describes to Juliet the pilgrim's kiss:
If I profane with my unworthiest hand
This holy shrine, the gentle fine is this:
My lips, two blushing pilgrims, ready stand
To smooth that rough touch with a tender kiss.
This repetition of the imagery depending from "holy" would constitute "iterative imagery" as it appears in more than one of Shakespeare's works. The study of iterative imagery might be thought of as a cross-reference comparison of imagery repeated throughout Shakespeare's corpus of work.