Christian Iconography could be a valuable resource. From Augusta State University, this work-in-progress is intended "to support the study of Christian iconography at the beginner's level." Its taglines are "Learn how to identify the saints in medieval and renaissance art. Read the stories that the paintings refer to. Find out the 'why' behind traditional elements in paintings of scriptural events."
You can enter a keyword to search for a particular iconographical element, or you can explore links on specific saints, topics, or selected scriptural events which are divided alphabetically. Each of these is illustrated by one or more images. There are also links to other sites useful in the study of Christian iconography, as well as a bibliography of recommended readings.
Image: euthman (Ed Uthman), Hans Memling: St. Veronica, c. 1470/1475, 2009. Available from Flickr under a Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic License.