out of copyright (called public domain in the USA), hence royalty-free stock image for all purposes usage credit requested Please do not redistribute without permission, since running this site is expensive.
Sacred Monogram, and Badges of the Apostles, from a Volume entitled, Francisci Nigri de Arte Scribendi, Daventrie, 1495.
I have made the four signs of the Apostles (the Gospel-writers) available as separate images, too: John, Luke, Mark and Matthew.
You can get a version of this image without the watermark at the lower right corner by requesting it here; The images are watermarked to help people find where they came from if they get reposted to blogs or other sites. Images under 1200 pixels on a side
are still free, although I will ask for a donation :-)