We know... That's why we need you. The image results that show up in the app are currently only the results that kind-of sort-of show up in the first five or six boxes of the search engine that is in use. It is a very simple search and that is why for example in the Spanish vocabulary list, for the word "uno", it looked like this:
Nothing in these images really represents the number "1" especially without giving the Spanish word away, which does not make a lot of sense... currently.
What is going to happen later in the app, is that when you, our users, search more and more images that remind you of the word "uno" the 7 (more or less) most popular images will show up here as our "popular images".
You can then chose to use one of these images, or of course simply search the web for any image that suits you... A unicorn perhaps? Unicorns always work... for any word.