Is is possible that this image changes with each page, but not randomly?
This code will change out the image. To limit it to a specific page, you would need to check the page source of the page you'd like to use it on and add the page ID to the front of the selector. For example, you would change "#masthead .thumbnail img" to "#page-id-2 #masthead .thumbnail img".
#masthead .thumbnail img {
display: none;
}
#masthead .thumbnail {
background: url(http://s.wordpress.org/about/images/wordpress-logo-notext-bg.png) no-repeat;
width: 176px;
height: 145px;
display: block;
-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=100)";
filter: alpha(opacity=100);
opacity: 1;
-webkit-transition: background 0.3s ease;
-moz-transition: background 0.3s ease;
-o-transition: background 0.3s ease;
-ms-transition: background 0.3s ease;
transition: background 0.3s ease;
}
#masthead .thumbnail:hover {
background: red;
width: 176px;
height: 145px;
display: block;
-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=90)";
filter: alpha(opacity=90);
opacity: .9;
-webkit-transition: background 0.3s ease;
-moz-transition: background 0.3s ease;
-o-transition: background 0.3s ease;
-ms-transition: background 0.3s ease;
transition: background 0.3s ease;
}
This code is a slightly different example I came up with while testing stuff out. It uses two images instead of leaving one as a background color and the effect with the example logo images I used turned out kinda cool:
#masthead .thumbnail img {
display: none;
}
#masthead .thumbnail {
background: url(http://s.wordpress.org/about/images/wordpress-logo-notext-bg.png) no-repeat;
width: 176px;
height: 145px;
display: block;
-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=100)";
filter: alpha(opacity=100);
opacity: 1;
-webkit-transition: background 0.5s ease;
-moz-transition: background 0.5s ease;
-o-transition: background 0.5s ease;
-ms-transition: background 0.5s ease;
transition: background 0.5s ease;
}
#masthead .thumbnail:hover {
background: url(http://s.wordpress.org/about/images/wordpress-logo-simplified-bg.png) no-repeat;
width: 176px;
height: 145px;
display: block;
-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=90)";
filter: alpha(opacity=90);
opacity: .9;
-webkit-transition: background 0.5s ease;
-moz-transition: background 0.5s ease;
-o-transition: background 0.5s ease;
-ms-transition: background 0.5s ease;
transition: background 0.5s ease;
}
These examples should help get you started. Note that you can take these and try changing around the options to get different effects.