I collect old photographs. This postcard was in a batch I've just bought from a dealer over the Internet. It appears to be a woman wearing mourning dress, though I've never seen this type of bonnet and veil before.
On the back of the card the dealer's written "early Edwardian", and there's a photographer's stamp; "Copyright - Lizzie Caswell Smith, 90 Gt. Russell Street, WC1".
Lizzie Caswell Smith is listed in the National Portrait Gallery's collections, but none of her photographs are shown online. Will have to check the next time I go there.