Ps. Only work with theme based in 1.8 default theme.
This is similar solution used in xenforo
1 - Create new file with name resizer.js in Notepad++
1.1 - Copy code below in resizer.js
PHP Code:
// jQuery.naturalWidth / jQuery.naturalHeight plugin for (already-loaded) images
// Triple-licensed: Public Domain, MIT and WTFPL license - share and enjoy!
(function($) {
function img(url) {
var i = new Image;
i.src = url;
return i;
}
if ('naturalWidth' in (new Image)) {
$.fn.naturalWidth = function() { return this[0].naturalWidth; };
$.fn.naturalHeight = function() { return this[0].naturalHeight; };
return;
}
$.fn.naturalWidth = function() { return img(this[0].src).width; };
$.fn.naturalHeight = function() { return img(this[0].src).height; };
})(jQuery);
$(document).ready(function() {
function imageLoaded() {
var resizelang = 'Click on this image to display the full size version.';
var resizedsize = $(this).width();
var origsize = $(this).naturalWidth();
if (origsize!=resizedsize) {
$(this).wrap('<div></div>').attr('title', resizelang).on('click', function() {
if ($(this).is('[title]')) {
$(this).removeAttr('title');
}
else {
$(this).attr('title', resizelang);
}
var parentheight = $(this).parent().height();
if (!$(this).hasClass('resize')) {
$(this).addClass('resize').parent().css('height', parentheight+'px');
}
else
{
$(this).removeAttr('class').parent().css('height', '');
}
});
}
}
$('.scaleimages img').each(function() {
if( this.complete ) {
imageLoaded.call( this );
} else {
$(this).one('load', imageLoaded);
}
});
});
3 - In ACP go to headerinclude template
3.1 - Find:
PHP Code:
<script type="text/javascript" src="{$mybb->asset_url}/jscripts/general.js?ver=1800"></script>
PHP Code:
<script type="text/javascript" src="{$mybb->asset_url}/jscripts/resizer.js"></script>
PHP Code:
.resize {
max-width: none !important;
position: absolute !important;
z-index: 20 !important;
}