I saw a butterfly in one of these three pictures. I didn't know how to categorise it. I marked it as 'reptile'.
Is that ok?
Just to clarify a bit more:
You don't need to worry about creatures (such as insects) that are completey outside the range of animals in the list. Just look for Mammals, Birds, and Reptiles. So in your example image, you would just need to classify the Wildebeest.
Of course, if the only thing seen in any of the images was, say, a butterfly, then you can do as sk001 suggests and classify it as "Nothing Here".
And you can always tag it with #butterfly here in Talk.