This is another festival where there are no shortages of images out there. Particularly in ancient art baptism is frequently portrayed as well as the baptism of Jesus. Also the reading from the New Testament is from the baptism of Corneilius, the Roman Centurion in Acts, so a couple images from the Acts story first:
Gerbrand van den Eeckhout, Vision of Cornelius the Centurion, 1664
Francesco Trevisani, Peter Baptizing the Centurion Cornelius (1709)
Guido Reni, The Baptism of Christ (1623)
Francesco Albani, Baptism of Christ (1600s)
A favorite for stained glass windows:
Louis Comfort Tiffany, The Baptism of Christ, Stained Glass Window at Brown Memorial Presbyterian Church, Baltimore
And icons
Baptism of Jesus, Orthodox Icon
And Baptism in general appears in artwork across the ages from the very ancient
Baptism Fresco on the catacomb of Saints Marcellinus and Peter, Via Labicana, Rome, Italy
Masaccio, Baptism of the Neophytes, (1424-28)
To modern architecture and art in churches:
Baptismal font at Valparaiso University
Descending Dove in Grace Lutheran Church, Tacoma Washington
Sign of the Rose 