yes... just did this...
go to your /gallery2/themes/***the theme you are using***/templates/theme.tpl
open that file and modify the line that reads:
<img src="{g->url href="images/galleryLogo_sm.gif"}" width="107" height="48" alt=""/>
you can either change the name of the .gif file to what you want and change the height and width and save tp "/images" folder - or if you make your own custom logo the same size as the original then you can name it "galleryLogo_sm.gif" and put it in your "/images" folder and it will use your logo on all the pages..... hope this made sence... it worked for me.