1) Load a square prop from the Library

2. Select the square, then go to the Material Room (CTRL-U).

3. Set Diffuse_Value and Specular_Value to 0. This turns them off.

4. Attach a 2D image map node to the Ambient_Color channel, as follows:

Left-click on the little plug icon next to Ambient_Color to get the popup menu.
New Node --> 2D Textures --> image_map

5. Load your jpg into the Image_Map node.

6. Set Ambient_Value to 1 for maximum brightness.

Now try rendering it and see how it looks.