I’ve rewrited the splitImageValue, I hope it will work in most cases.
I had to test wether the URL contains /media, for the category image

	/**
	 * Splits images Path and Name
	 *
	 * Path=custom/module/images/
	 * Name=example.jpg
	 *
	 * @param string $imageValue
	 * @param string $attr
	 * @return string
	 */
	public function splitImageValue($imageValue,$attr="name"){
		$imArray=explode("/",$imageValue);

		$name=$imArray[count($imArray)-1];
		$path=implode("/",array_diff($imArray,array($name)));
		if (strpos($path, Mage::getBaseUrl('media'))===0){
			$path=substr($path, strlen(Mage::getBaseUrl('media')));
		}elseif(strpos($path, Mage::getBaseUrl())===0){
			$path=substr($path, strlen(Mage::getBaseUrl()));
		}
		if($attr=="path"){
			return $path;
		}
		else
			return $name;

	}

I would love to implement this helper, but I don’t know where to start. Could you point me in the right direction where to put this code to make it work? I need to resize my category-images.

Thanks in advance!