Image width auto not supported

I'm working on a function wich renders dynamic PDF evaluations content, the problem I have is with images, I don't know the width or height of images, so i'm trying to set style width to 'auto' but it doesn't work, the image always fits the page width.

Please, could you add support for set image width to 'auto' in order to keep images with their natural width in case we don't specify dimenssions.

The image placed is small but fits 100% page width, instead of keeping its natura width (or height).