After much searching and Database queries I found a forum post that explains how to add a url rewrite rule to make all images on a gallery2 site have a watermark. I’m sure also with some massaging it can be applied to different albums, but all I need is all or nothing.
Find the /main.php view note what is before /main.php if anything and replace with second line making sure info before /main.php is intact.
# RewriteRule . /gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=%1&g2_serialNumber=%2&g2_fileName=%3 [QSA,L]
RewriteRule . /gallery2/main.php?g2_view=watermark.DownloadItem&g2_itemId=%1 [L]
Note: This is also a reference for myself who always forgets stuff like this months later.