Purchase a canvas to which you would like to adhere your picture. If you are adhering a photograph, print that photo the size of your canvas. If you're attaching an art project, purchase a canvas that is the same size as your art picture. If you can't find the perfect size, purchase something slightly larger over a canvas that is too small.
Use your paintbrush to coat the entire front of the canvas with a thin layer of acrylic.
Paint the back of your photograph or art picture with acrylic.
Lay your picture down on the canvas, adhering it into place. Be extra careful to make sure you get the picture on straight the first time. Acrylic dries fast, so you may not have a chance to fix a mistake if you don't move quickly.
Smooth down any wrinkles in your photo with your fingers, and paint over top of your art picture with the acrylic. Make sure to paint strokes from top to bottom and left to right to ensure you don't end up with any lines on your final product.
Allow your canvas to dry overnight, and hang your picture up for the world to see.