The British Library here and the entire collection of The Commons here.
Applications for Education
The Commons was already a good place for students and teachers to find public domain images (mostly of a historical nature) and the addition of The British Library's images makes it even better. I've used images from The Commons in my history classes as prompts for discussion and my students have used them in short documentary videos they've made.
To go beyond visual artifacts you may want to explore The British Library's Sound Maps.
Over the weekend many blogs have covered this news from The British Library. I first saw the announcement from a Tweet from Jen Deyenberg.