When William Thompson Walters, a successful 19th-century Baltimore businessman, willed his extensive art collection to the city “for the benefit of the public,” he couldn’t have foreseen how closely it would adhere to his wishes. For almost two years now, Baltimore’s Walters Art Museum has been putting classic paintings from the collection in very public, very outdoor places. More than 30 reproductions have been installed throughout the city -- from the Maryland Zoo to just outside the entrance to city hall -- in an effort to increase awareness of the museum. Walters himself opened his house and the collection within once a year to anyone who could afford the 50-cent price of admission, donating the annual take of $30,000 to the city’s poor. The idea for the current Walters’ project, called “Off the Wall,” came from the Detroit Institute of Arts Museum, which launched its “Inside/Out” program three years ago. Since then, there have been similar ventures in Delaware, Michigan and Ohio. The popular open-air exhibition, which was originally slated to end in January, has been extended indefinitely. The program is being expanded to nearby Howard County, where six reproductions will be placed this fall.