If you have a Kindle, you could also try Kindle Unlimited. It's $10 a month, but they often have deals where you can get 3 months for $5 (and then cancel, if you want). I don't know how many picture books are available through the service, though, so you'd want to check that part out first. (It's essentially like a library -- for the monthly fee, you can read as many Kindle Unlimited books as you like. But that's why you'd need to be sure they have picture books that work for your purposes.)