Images with two states

I am new to Storyline and have been watching the tutorials on this site. One that I watched was: https://community.articulate.com/series/getting-started-with-articulate-storyline-2/articles/creating-a-drag-and-drop-interaction

In that video, it shows how to make an interaction where the door on the refrigerator opens and closes and the narration notes that this is simply through the use of an image with two states.

Does anyone know of a site or free repository online that includes a collection of images with multiple states so that more interactions like this could be built easily? 

Thanks.

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