I use http://typo3.org/extensions/repository/view/aus_driver_local_cdn as File Storege Driver.
So the image uri is http://cdn.mydomain.tld/my-image.jpg but the ImageViewHelper encodes the uri so my image.source is http%3A//cdn.mydomain.tld/my-image.jpg . The problem is in the preprocessImages and the preprocessSourceUri-method in the FluidTYPO3\Vhs\ViewHelpers\Resource\AbstractImageViewHelper, there is no check for a fully qualified uri

$imageSource = $GLOBALS['TSFE']->absRefPrefix . GeneralUtility::rawUrlEncodeFP($imageInfo[3]);

to

if(GeneralUtility::isValidUrl($imageInfo[3])) {
    $imageSource = $imageInfo[3];
} else {
    $imageSource = $GLOBALS['TSFE']->absRefPrefix . GeneralUtility::rawUrlEncodeFP($imageInfo[3]);
}