One of the more famous quotes is "a pictures paints a thousand words". As the interwiki bot is running again, I do check every now and again its work. When I look at the entry [[ラッコ]], you will forgive me that it is Japanese to me. However, the picture that can be seen allows me to translate it to "zeeotter".
Pictures are great. We do need them with the WiktionaryZ content. Having said this, the fun starts. We can decide to allow only for pictures that can be found in Commons. There are precedents for it. It solves the problem of what upload rules would be allowed; they would be the strict rules of Commons.
The other thing you would get into are the illustrations that are problematic for some cultures. In my country, people have as many genitalia as in any other, they look more or less the same as in any other, they are as rare as in any other and a picture would not be problematic. In many countries this cannot be done. One great example of this can be found here. Now when you read this in some 10 days time this picture may not be there anymore. It does however show you the sensitivities that need to be considered with pictures.