First, sorry if my vocabulary is wrong, I am more used to Gimp and Inkscape to be honest, these are my first steps with Blender :D What I would like to render is some kind of perspective screenshot. What I mean is that I have an 2D image that I have put on a plane and I want to create the render of this image not only like if it was taken by a camera with an angle, but this camera would be set as if the focus would be on some part of the image (so the part of the image that is "too close" or "too far" would be rendered as blurred). That's were my vocabulary is limited… a real photograph example would be this.
For now what I've managed is to create the plane and to tilt it in a way the camera is showing an interesting perspective. Then I use "Render/OpenGL Render Image" but the whole image is perfectly clear. If anyone has a tip or a tutorial to propose, I would be extremely thankful !