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You may have a LOT of cross-browser issues to deal with. &nbsp;Have a look a this: 
<a href="http://www.quirksmode.org/css/overflow.html" rel="ugc">http://www.quirksmode.org/css/overflow.html</a> 
 
HTH, ~Ray
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Also this: 
<a href="http://www.w3schools.com/Css/pr_pos_overflow.asp" rel="ugc">http://www.w3schools.com/Css/pr_pos_overflow.asp</a>
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id recomend either: 
educating your admin users to upload correct sizes and add a check on the upload that only allows correctly sized images; 
add an image resizing component to your admin; 
 
to address your actual question, does the javascript tool resize the divs? as usually a background image will not 'push' a div so overflow issues should not be an issue.
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You could write a PHP script utilizing the GD extension (although it must be installed with your php installation) to automatically get the size of the image, and if it is beyond x width and/or y height, then resize it to a new x width and y height. 
 
To maintain proportion, &nbsp;you could resize based on percentages, applying the calculated percentage to both x width and y height. 
 
The GD &lt;a href=&quot;<a href="http://us2.php.net/manual/en/ref.image.php" rel="ugc">http://us2.php.net/manual/en/ref.image.php</a>&quot;&gt;documentation&lt;/a&gt;
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This function will resize an image. ~Ray 

<pre><code class="code-10 nolinks" id="code-210471">/* ********************************************************************************************* */
/* comment lines will work if GD2 is not installed, but will make poorer images */
/* */
// MAKE AN IMAGE INTO THE RIGHT SIZE FOR PAGE DISPLAY
function create_right_size_image($image, $width=720) {
 
	$source = imagecreatefromjpeg(&quot;$image&quot;);
 
	$imageX = imagesx($source);
	$imageY = imagesy($source);
 
	if ($imageX &lt;= $width) {
return FALSE;
}
	if ($imageX &gt; $width) {
		$tnailX = $width;
		$tnailY = (int) (($tnailX * $imageY) / $imageX );
	} else {
		$tnailX	= $imageX;
		$tnailY = (int) (($tnailX * $imageY) / $imageX );
	}
 
	$target = imagecreatetruecolor($tnailX, $tnailY);
//	$target = imagecreate($tnailX, $tnailY);
	imagecopyresampled ($target, $source, 0, 0, 0, 0, $tnailX, $tnailY, $imageX, $imageY);
//	imagecopyresized ($target, $source, 0, 0, 0, 0, $tnailX, $tnailY, $imageX, $imageY);
 
return $target ;
}
/* ********************************************************************************************* */
</code></pre>
</div>

<div>
Sample calling sequence where $my_new_file is the path to the image in the server file system. 
 
HTH, ~Ray 

<pre><code class="code-1 nolinks" id="code-210473">// RESIZE THE FILE TO FIT WIDTH, IF NECESSARY
if ($imageblob	= create_right_size_image($my_new_file)) 
{
 imagejpeg($imageblob, $my_new_file);
}
</code></pre>
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<div class="content wysiwyg-content">
I have a div that is 600 x 400px. I have a javascript tool that is a gallery it work by changing the background image of the div. 
 
My image is bigger than the div tho, I dont want the div to resize I want the image to fit it without losing proportion. How can I set the background-image of the dive to be no larger that 375px in height. 
 
The images in the div are of various sizes but as this is powered by a simple CMS the images can be of various sizes as the users may not upload small sizes. 
 
Thanks
</div>
</div>

I have a div that is 600 x 400px. I have a javascript tool that is a gallery it work by changing the background image of the div.

My image is bigger than the div tho, I dont want the div to resize I want the image to fit it without losing proportion. How can I set the background-image of the dive to be no larger that 375px in height.

The images in the div are of various sizes but as this is powered by a simple CMS the images can be of various sizes as the users may not upload small sizes.

Thanks

Resizing a background-image in a div

Cascading Style Sheets (CSS) is a language used for describing the look and formatting of a document written in a markup language. Usually used to change web pages and user interfaces written in HTML, it can also be applied to any kind of XML document. CSS is designed primarily to distinguish the content of a document from its presentation.

HTML (HyperText Markup Language) is the main markup language for creating web pages and other information to be displayed in a web browser, providing both the structure and content for what is sent from a web server through the use of tags. The current implementation of the HTML specification is HTML5.

HTML

PHP is a widely-used server-side scripting language especially suited for web development, powering tens of millions of sites from Facebook to personal WordPress blogs. PHP is often paired with the MySQL relational database, but includes support for most other mainstream databases. By utilizing different Server APIs, PHP can work on many different web servers as a server-side scripting language.