Using images in translation messages (here advancedsearch-help-category) has impact for the translator, because the translator has to ignore the part of the message and in most case the <img> does not play nice with screen reader, because it does not provide an alt text by default. All wikis using this file must also have commons as a image repository to find the image and display it. It also needs a network connection for the people viewing the page, which may not active when using a intranet wiki.

For extensions it is much easier to create a stylesheet and load the image with a stylesheet from the extensions directory or from a dependency repository, but please do not load images from a shared repositiory which is not part of the default config. Stylesheet could also benefit from embedded images to speed up load time.