After a while I thought to put some of my pluings I have made months ago on my blog and WP plugin repository , so here is it one of the basic plugins The WordPress Login Logo Changer .
It is a very simple pluing to change the logo of login screen, just download & install it
Some basic steps you should follow are
Download the WordPress Login Logo Changer By Ahmad Awais , and install it by upload its zip to wordpress
You can directly upload your plugin zip file by clicking on Upload:
Use the browse button to select the plugin zip file that was downloaded, then click on Install Now. The plugin will be uploaded to your blog and installed. It can then be activated (see Automatically Installing a Plugin).
Goto your activated theme’s images folder (if not present create one it will be here yourdomain.com/wp-content/themes/yourtheme/images) and put your logo of dimensions about 325* 85 and the name of that logo must be login_logo.png.