Look for the works of Renaissance painters, particularly those who painted portraits. To familiarize yourself with this period in art, try the Grove Dictionary of Art's entry on the Renaissance. Then look up the artists mentioned in ARTstor. You might also be interested in looking up the artists in the library catalog, as we have many books of images of the works of Renaissance artists. Some books of interest, with many examples of Renaissance portraits: The Renaissance portrait: from Donatello to Bellini, Pontormo, Bronzino, and the Medici: the transformation of the Renaissance portrait in Florence, and Renaissance self-portraiture: the visual construction of identity and the social status of the artist. The links lead to the catalog records for these books, giving you the call number and status (checked in, checked out).