//http://detectmobilebrowsers.com/
//more
//more...


<?php if ( is_mobile() ) {   
    the_post_thumbnail( 'small' );  
} else {  
    the_post_thumbnail( 'large' );  
}; ?>  

//ie detection

<?php if ( is_IE() ) { 
	$browserInfo = php_browser_info();
	$browser = $browserInfo[browser];
	$version = $browserInfo[version];

	echo '<div class="browser-notification">You are using '.$browser.' '.$version.' . Please, update your browser for better experience.</div>';
}; ?>



<?php
//http://wpsnipp.com/?p=1131
function mv_browser_body_class($classes) {
                global $is_lynx, $is_gecko, $is_IE, $is_opera, $is_NS4, $is_safari, $is_chrome, $is_iphone;
                if($is_lynx) $classes[] = 'lynx';
                elseif($is_gecko) $classes[] = 'gecko';
                elseif($is_opera) $classes[] = 'opera';
                elseif($is_NS4) $classes[] = 'ns4';
                elseif($is_safari) $classes[] = 'safari';
                elseif($is_chrome) $classes[] = 'chrome';
                elseif($is_IE) {
                        $classes[] = 'ie';
                        if(preg_match('/MSIE ([0-9]+)([a-zA-Z0-9.]+)/', $_SERVER['HTTP_USER_AGENT'], $browser_version))
                        $classes[] = 'ie'.$browser_version[1];
                } else $classes[] = 'unknown';
                if($is_iphone) $classes[] = 'iphone';
                if ( stristr( $_SERVER['HTTP_USER_AGENT'],"mac") ) {
                         $classes[] = 'osx';
                   } elseif ( stristr( $_SERVER['HTTP_USER_AGENT'],"linux") ) {
                         $classes[] = 'linux';
                   } elseif ( stristr( $_SERVER['HTTP_USER_AGENT'],"windows") ) {
                         $classes[] = 'windows';
                   }
                return $classes;
}
        add_filter('body_class','mv_browser_body_class');
?>