Search online for a black and white vector image to use in your design or draw a design yourself if you have the talent. Take the image to a local printer or office supply store with an office center and have it sized to 20-by-30 inches and printed on a large format printer capable of printing poster-sized prints.
Purchase a 24-by-36-inch blank white canvas.
Purchase a jar of acrylic paint in your choice of color from an art supply store or hobby supply store or have a small jar mixed to your custom color preference at a paint store or home improvement warehouse.
Paint the entire canvas with the acrylic paint. Allow the canvas to dry until it is no longer wet to the touch.
Cut out the image that you had printed based on how you want to appear at the end of the project and attach it to the painted canvas with decoupage. Use a plastic squeegee to smooth out any bubbles in the the image. Allow the decoupage to dry completely.
Cover the entire canvas with a coat of varnish to help blend the image into the painting and to reduce the shine of decoupage.