I have created a toolkit for the script retinaimages.php. The script loads higher resolution versions of images if they are exists. For me it works. I would be nice if a more expierenced hiawatha user have a look on it. If it is OK I would like to send it the developer of retinaimages.php. Perhaps he can add it to the existing examples for apache and nginx.
UrlToolkit {
ToolkitID = gotoretina
Header COOKIE devicePixelRatio=1 Goto retinaimages
}
UrlToolkit {
ToolkitID = retinaimages
Match .+(gif|jpe?g|png)$ Rewrite /retinaimages.php
}