Possibly because the author needs to include appropriate <allow > tags in the XML for the specific images. These tags are generated automatically for "non-dynamic" <img > tags but not for dynamically specified ones.

Thus, for example:

<img src="/res/domain/name/subdir/$variable.gif" /> will cause the tag

<allow src="res/domain/name/subdir/$variable.gif" /> to be automatically generated and appear just prior to the </problem > tag. However, that is non-functional because there is no specific image having that name. (It would probably be better if it were not generated at all.) The author will have to hand-generate an appropriate allow tag for any images that may translate to $variable.gif.

A global specification such as <allow src="/res/domain/name/subdir/*.gif" /> seems to work OK.