so, ways to get around this:

turn off AI results. they're literally nonsense to us

don't use pinterest because the sources/provenance is often hard to trace

a standard internet search can be okay, but museum collections are the top tier (list of collections below this list)

instead of broad terms like victorian, regency, tudor, renaissance etc. try using the decade you're looking for. if you're not sure of what decade it is but have a vague image in your head, look on the fashion history timeline and just jump around until you find it. but even changing to e.g. 19th century will give better results than victorian

including terms like womenswear/menswear, daywear, formal wear, evening wear, court dress should increase the value of your search too

including "fashion plates" in your search can give you a nice impression of the intended silhouettes of the era. some of these might be a little stylised but will show you what was considered in vogue

for pre-fashion plate eras or things like makeup and styling, you'll have to look at portraiture or manuscripts. these are harder to actually find what you're looking for, but searching museum collections and limiting results to specific date ranges will be your friend

when looking at art, do bear in mind sometimes artists would paint fabric extra flow-y to show off their skills. it might not have been exactly like that in terms of fabric weight or drape. so, a pinch of salt required!

if you find something on image search where the provenance is dubious, reverse image search and you might find a source! i've been able to trace random pinterest images to real sources, but this does take a lot of time and effort and is often not worth the headache

some online resources and museum collections:

fashion history timeline is an invaluable resource if you're trying to get a feel for everything and should be your first port of call. it'll also link to good examples

the met has a vast number of extant examples of clothing, as well as fashion plates

costume institute fashion plates is a subcollection of the met for fashion plates (1800s-1922)

v&a also has many extant garments, fashion plates, and incredible articles on clothing and aesthetics. read the details of the objects because they'll often reveal a lot about the piece

lacma is good for C19th-20th pieces

nypl digital collection for photographs

national portrait gallery or similar for portraiture, or literally any museum in your country that has historical art

national museums scotland can be useful situationally but might be oddly specific

stout style history is a great collection for finding image references for fat people wearing historical clothes. survival bias of a lot of museum pieces tends towards smaller clothing that couldn't be repurposed, but this aims to counter that. it's not sortable, but is still a really nice resource

wikimedia commons is surprisingly handy! and the images, if you should need to link/repost them, are public domain

auction websites sound like a funny one to recommend. some won't have mannequins and some will. just look up historical garment auctions and you'll find some!