You need to do UV projections and then use the UV texture editor to take the snapshot.

Select the faces you want to paint e.g. the top ones then go to the orthographic viewport that lets you seem flat on.

Then go to edit polygons>>texturing>>Planar Mapping (options box) and select Mapping direction "from camera". then click project.

Then go to window uv Texture editor and you should now see the faces that were projected. You can then repeat this process as necessary and then edit the UVs into a flat image and then use the UV snapshot thingy to get the picture to paint.

There are loads of tutorials (video ones on this site!) to find a better explanation of this process.

Alan