Hello Tatiane, I don't know if there are more specific, dedicated repositories for animal pictures, but often the best resource is using the Creative Commons' search tool: https://search.creativecommons.org/
It facilitates searches on 15 different search engines using their built-in licensing tools; so if you enter "animals" and select Flickr, it will take you to the Flickr website with "Commercial Use & Mods allowed" filter activated. You still need to look at each item to verify the specific terms of the license - whether attribution is required (it's generally best practice regardless) and whether you must include the same terms for any adaptations (don't try to trademark something you've downloaded and then modified) - but you will have access to an array of no-cost visual assets. For more details about the kinds of licenses, have a look at Creative Commons' page "about CC licenses": https://creativecommons.org/share-your-work/cclicenses/
Thank you so much for your answer!
I'll take a look at the links you recommended.
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