Adding Avatar Icon / Functions.php Error

I have been tweaking a blog for my newborn son and I wanted to look into changing out the standard mystery man avatar on all of the comments. I found a walkthrough on a site that had a PHP code to add to the functions.php area of the theme. Adding this, it said would pull whatever custom image from the images folder was titled correctly to match the code.

I added this code under the default code in the functions.php section and hit Update File. All of a sudden I get a warning at the top above the Dashboard saying:

Warning: Cannot modify header information – headers already sent by (output started at /home/content/P/i/g/Pigsel26/html/senate/wp-content/themes/strange-little-town/functions.php:13) in /home/content/P/i/g/Pigsel26/html/senate/wp-includes/pluggable.php on line 850

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It repeated this twice and every page had it. I logged out, tried to enter again. Same thing. I emptied my cache and even restart Safari, same thing. The site is running fine, but I can’t access the login screen or Dashboard at all now.

I am in desperate need of help. I don’t want to lose any of this information.