Finding cosplay pictures of a character on Instagram: Good luck with that, because you can only search by one tag at a time, and people post so many screen grabs, scans, memes & spam that you can’t find the costumes.
Finding cosplay pictures of a character on Flickr: Good luck with that, because even though you can do a full-text search of the title, tags & description, people upload all 400 photos from the weekend as DSC8764.jpg to DSC9163.jpg and only tag them with the convention name.
Also, it doesn’t help much to search for “Flash” on a photography site, particularly one where the people who *do* tag their pictures often add the settings they used for each photo.