In February 2011, the possibility to add images to OmegaWiki was implemented. A few months later, we have already more than 1000 images. Images help to understand definitions and are an important feature of (online) dictionaries.
In OmegaWiki, when an image is added, it is attached to a particular concept, and is then displayed for all words representing that concept. Compared to Wiktionary where you would need to add an image of a concept for each page of each synonym, and for each page of each language, there is a lot of redundant work that is avoided.
As of today, there are about 47.000 concepts in OmegaWiki. It means that more than 2% of them have an image. It is not clear what percentage can be reached. Several concepts are abstract (feelings, reasonings), and other are verbs or names of languages and are hard to illustrate.
I find it particularly useful when a word with different meanings has different images, such as vampire, bluebottle, Mars, Venus, etc. Also interesting is to find an illustration for abstract concepts. This is sometimes possible: season, wake up or cheapskate.
P.S.: we have also almost 15.000 links to Wikipedia articles :-)