As a collector of old glass plates, I have many hundreds from France, I don't think I ever found one of that age in that type of envelope, all mine were generally boxed and labelled. The writing on the envelope appears very modern and the term Photocrom definitely doesn't refer to this type of photography. When the plate is removed from the envelope, whilst partly obscured by the hand, the subject appears to be written as Cat, odd given this is a French speaking part of the world. The images themselves are just too sharp, even in full daylight those animals would have had to remain perfectly still for some time to achieve this result with the camera equipment available at the time. It all just seems to convenient given the posters background. And just to be nitpicky, surely the title of this should be "Prints Glass Plate Negatives" given no developing takes place, the plate is already developed?I'm not so sure about this for several reasons.