I totally understand where you’re coming from, because it has taken me such a large number of hours to do the fish course this way.
Personally I felt strongly enough about it that I left a lot of species out if I couldn’t find several photos of different individuals of the species, which meant that there were species I didn’t add when I first added their families even though I wanted them in the course, and some of those I eventually got around to many months later. One way to handle the workload is simply to spread it out over years like that.
If I were doing a course on North American birds (which I have considered doing and may do sometime), I’d probably ask the Cornell School of Ornithology for help finding images with appropriate rights. Maybe they can help with southeast Asian birds, or know of another institution that can help? It’s worth asking them.
Wikimedia Commons has been a very useful resource for me, and probably would be for you, but I agree that it does take significant time to use. I’ve found that it’s much more effective to skip Wikipedia, though, and go right to commons.wikimedia.org. Search for the scientific name of the species in the search bar at top right. Sometimes you find nothing, or only one, but sometimes you find a lot. And even if you find only one or two, that can be a great supplement for a species that you only had one or two photos of before.
Since most Wikimedia images are CC BY, requiring attribution, I use OS X’s “Preview” (what you get by default when you double click on an image file) to add text to each image with an abbreviated form of the attribution text from Wikimedia. For example, if the wikimedia attribution text is “By Paul Asman and Jill Lenoble - yellowtail parrotfish Sparisoma rubripinneUploaded by Amada44, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=25258404” then I will edit that down to “Paul Asman and Jill Lenoble - CC BY 2.0”, or if there’s room on the image to comfortably fit a bit more text, “Paul Asman and Jill Lenoble - CC BY 2.0 via Wikimedia Commons”.
BTW, one really frustrating thing about one of the bird courses I take online, aside from it having only one picture of each species, is that the watermarks on some of them identify the species! Be careful, it’s easy to do that by accident - notice that would’ve happened here if I’d just copied the text from Wikimedia without thinking about it too carefully, since the title of a photo often includes the name of the species it’s of.
It was really really helpful to me to find, when I started, a couple of sites that were one photographer each, who could give me permission to use any photos from their site. If I hadn’t found those two sites, I would have started with my own photos only, which means I would’ve started with a much smaller number of species and taken a lot longer to ramp up initially. With that in mind:
Can you find a web site that has a lot of photos of birds you want in your course, all from the same photographer? A photographer’s own site, perhaps intended as a bird guide?
Do you know someone who’s interested in birds and recently gone to, or is planning to go to, southeast Asia to see and take pictures of birds? Maybe your friend/acquaintance would let you use their photos?