Good news. The New York Public Library has just added hi-res versions of tens of thousands of its public domain digital holdings and they invite you to use them however you like. Print and frame them for your walls, work them into homemade party invitations, basically, use and remix them to your heart's content. Here are a few of my favorites:
A vibrant blue cyanotype would be striking to frame for your wall. See dozens more in the Photographs of British Algae: Cyanotype Impressions collection.
Looking for something more decorative? How about a botanical by prolific illustrator Pierre Joseph Redouté. There are hundreds to choose from in the Les liliacées collection.
These charming oddities are part of the R.H. Burnside Collection focused on costumes. Make a sign for your desk with one image on each side and let your co-workers know what kind of a mood you're in.
Jersey, you never looked so good. There are so many cool old maps to peruse - try searching for some of your favorite places. Framing a special one would be a lovely gift for a friend of family member.
These goofy and endearing photographs from the A.G. Spalding Baseball collection would be a fun addition to a gallery wall display.
I love NY, do you? The Pictorial Description of Broadway collection contains nearly a hundred drawings depicting each block of turn of the Century Broadway. Print a bunch and line them up side by side, perhaps like a wallpaper border in a small room.
Feeling inspired? Visit the NYPL Digital Collections and find your own treasures.