Greetings everyone, occasional lurker here.

I am looking for images of barding that predates plate armor. I have had no luck searching for information on horse armor because of how famous and ubiquitous certain specimens are. Any search term will bring up the well-known plate variants, which it seem still inspire a lot of skepticism that they were light enough to be used on the battlefield by fighting men, as opposed to highly-visible (and wealthy) commanders.

Such as: http://c7.alamy.com/comp/ENWJTN/armor-for-com...ENWJTN.jpg

Specifically, I am interested in maille and quilted defenses for the chest and body. This book was interesting, but just a start:
https://archive.org/details/recordofeuropean03lakiuoft

It is my understanding that from the 13th Century on, many armies encouraged or expected their men-at-arms to ride armored horses. At the same time, actual depictions of armored horses in battle scenes are relatively rare.

I recall various examples of full-length caprison-type maille defenses for horses, sometimes depicted in videogames:
https://vignette.wikia.nocookie.net/mountandblade/images/a/a4/Warhorse.jpg/revision/latest?cb=20090530142631

Does this amount of mail also inspire skepticism in modern researchers? It certainly appears restricting and massively expensive, especially in the 1200s.

Surely a more modest armor design, such as a maille 'peytral', would provide better 'bang for your buck.' Specifically I can imagine how a relatively small amount of frontal armor would enable a determined knight to crash into a line of infantry with the confidence that the horse would not impale itself on a dagger. Because without that armor, it seems that even a formation of armed manikins would prove highly lethal to a charging destrier. One lance thrust by the rider can't prevent the horse from collision with a sharp weapon.

Does anyone have any insight to share, or just examples of maille and textile horse armor with modest (or not) coverage of the head and body?

Horses wore armour continuously for a period of over three thousand years starting around the 15th C BC. You need to narrow down your time period and region before you can get a sensible answer.

It was used, also on the battlefield. Same goes for plate horse armour, that was also used. I'm not an expert when it comes to the 13th and 14th century. In the 15th century however we see leather armour for horses first, until around 1470-1480 the first plate armours show up. The one from Friedrich III. being an exception that is an earlier piece. In most manuscripts you see leather armour that has been painted or covered with fabric. Arne Koets knows sources from 16th century Netherlands that talk about breaking pike blocks with heavy cavalry, where the first line uses armoured horses.
Aside from that, manuscript miniatures delivers quite a bit of pictures.