Most definitely think every photo should be credited. I use stock photo from time to time to do art journal, but I tend to scrap our lives so, rarely use them, still, I understand some people love them, nothing wring with that, but if it is a stock photo, it should be noted.
I know Pixabay doesn't require to credit the photographer, but as I understand, you need to mention the site.
I know many scrappers who do credit., especially Pixabay and Unsplash, I think crediting the photo should be requirement in every gallery.
I'm a crazy obsessed, credit down to the staple, which sometimes can be time consuming, but is the way I feel, like I feel about music not being credited properly
So yeah, most definitely not alone on this one, Angie