Images can be posterized using the built-in Posterize command, but it provides little control over the process. An alternative means was used here. After routine adjustment with Curves, the library image was copied onto a second layer. The Find Edges filter was applied to the copy layer and that layer was then desaturated. Contrast was accentuated using Threshold, and the two layers were blended using Overlay.

The building to the left of the Library was removed and the left border of the Library building was patched in several areas using the Rubber Stamp tool. The background sky was selected and the selection then inversed, leaving the Library building selected. The building selection was made into a path, and the path was made a clipping path.

A new document was created in Illustrator where the Photoshop file was placed on its own layer. In Illustrator, additional layers were created for the background color, the title, the quote from Wadsworth, and the frame.
To create a Web version, the composite Illustrator file was opened and rasterized in Photoshop and then output as a GIF.