That's a watermark logo. There are tons of videos in YouTube about how to insert watermark in photoshop and other software. If you don't have access to photoshop, you can find other software that automates the watermarking process.

If you're using photoshop, Russel Brown's website is pretty good for tutorials about how to watermark images. Here's the link;
http://www.russellbrown.com/tips_tech.html

Otherwise, google around for other software.
I just found this site (says its free!!).

Peace.....