I can see once way to insert an image in the "body" (document) of an item: just enable the editor, right click and choose Image. That allows you to browse and find the image you want to insert.
There may be other way, but I don't seem them. For example
1. drag and drop onto the item
2. paste from the clipboard
#1 is handy, but not essential. But not being able to paste from the clipboard seems odd.
Of course it may be in Zoot somewhere...