Would it be useful for you to know the category of animal, such as antelope, even though we don't know the exact species? Is there a way to record this?
I think the scientists would like you to make a best guess if you know it's an antelope - not too many left to choose from. Remember others will also see each picture, and the aggregate opinion should be fairly accurate.
See the following blog for a better explanation: http://blog.snapshotserengeti.org/2012/12/14/we-need-an-i-dont-know-button/