in this topic 

i will try to show you how to change your login page

like this one مجتمع المرأة العربية <==  click here

soooo easy just do this following step 

1 : log to your control panel 

2 : go >   APPEARANCE > EDIT THEME > CSS 

3 : in the edit CSS bare past this CSS CODE

<--------DONT COPY THIS---->

.ow_sign_in_cont {

width:100%;height:100%;position:absolute;top:0;left:0;background: url('http://2.bp.blogspot.com/-GTrzmYmWL7o/UbxywlFVQmI/AAAAAAAAA8U/_CeNSyD_Xno/s1600/abstract_0001.jpg')no-repeat center center fixed;   -webkit-background-size: cover;  -moz-background-size: cover;  -o-background-size: cover;  background-size: cover;}

<--------DONT COPY THIS---->

and you have to change this link 

http://2.bp.blogspot.com/-GTrzmYmWL7o/UbxywlFVQmI/AAAAAAAAA8U/_CeNSyD_Xno/s1600/abstract_0001.jpg

and 4 : save