What you are seeing in the "sample2.png was made using css. All I did was to identify the class of the background and css it to background image.
HINTS:
* The background class = .ow_sign_in_cont (in base.css)
In my own case, these are my css declarations:
.ow_sign_in_cont {
width:100%;
height:100%;
position:absolute;
top:0;
left:0;
background: #75C5F0 url(images/signin.png) no-repeat;
background-size: 100%;
z-index:97;
*Just create your own background image and put inside your theme's image folder and declare it in background of your css.
Hope this help.