Another collection to add to the rounds! Wellcome Images is a part of the Wellcome Collection, a terrific, quirky-yet-intellectual museum located in London (I highly reccomend a visit--it's free, too!). The site encompasses a huge number of photographs, "with themes ranging from medical and social history to contemporary healthcare and biomedical science" (Source). While on the one hand it is a commercial image library, specializing in medical images, they've also recently released a large number of historical images, available for free creative commons use. This is what we like to hear!
Anyway, so these are the fruits of my first jaunt into their holdings-- some terrific health and safety posters created by the British Royal Society for the Prevention of Accidents (which apparently still exists under that great name). Unfortunately, as this collection is image-based, very little contextual information is given, not even dates. Visually they look quite a bit like WPA posters and WW2-era British posters, so my guess is late 1930s to late 1940s, but I'm not at all a poster expert. Mid-century, almost certainly.