Inside images folder you will find a file called sprite_v12.png open this with any image editing program and zoom in at the top you will see two text "Your Logo" the white one is the default and the grey is shown when you hover your mouse over your logo edit those two to your website logo but be careful! it MUST be in the exact same place as the default ones if its not your logo will not be shown or will be half!
save and exit
Now find a file colled watermark.png inside your images folder open it with any image editing program and change it to your website name eg. 9gagclonescript.com this will be show at the top right corner of every image!
there is also another image you should edit called 9gag-logo-large,png this is shown at registration and login page edit it to whatever you want