See http://xep.xattic.com/xep/testsuite/usecases/image-scale.pdf

Image width and height are already set in the image url, but they cannot be compliante with the available width of the PDF, especially if the PDF is displayed in 2 columns.

So width and height should be not specified as attributes, and content-width="scale-to-fit" should be used to ensure that the image will not exceed the available space