In phpBB by default it will use phpBB logo as your website logo at the top left corner of your page. You will be able to change the logo, file type of the image logo as well the size of the logo according to your own interest. Changing the phpBB site logo is simple enough. In this example, i will use one of styles installed in the phpBB which are subsilver2. Below is the step that you need to follow.
1. using FTP, go to your phpBB folder -> Styles -> Subsilver2 (Style used) -> imageset.
2. Notice that the default site logo name is site_logo.gif. You may change the image site_logo.gif to your like directly to change the site logo and you are done
If you prefer other file type image instead of gif or you might want to change the size of logo, continue to step 3.
3. In the same folder which is imageset, there will be one file named as imageset.cfg. Find the line which stated as follow:
img_site_logo = site_logo.gif*94*170
4.Change the site_logo.gif to your own image filename. 94*170 is the height and width of the image. Set it according to your own image.
5. Save the file. Go to your Administration Control Panel (ACP) -> Styles -> Imagesets. Click on refresh for the styles that you used which in this case is subsilver2.
That’s all. You should be able to see your new site logo at the forum board.