I have finished making the free-standing 'wall' to photograph artworks. It is 2.44m x 1.83m (roughly 8' x 6'), consisting of three half-sheets of 12mm MDF mounted to a softwood frame. The side struts are on small castors to make it easier to move around. The whole thing is bolted together using coach bolts and wing nuts so that it can be assembled without tools. A few little tweaks would make it even more straightforward to assemble and disassemble, but it's not bad as it is. The joins between the panels are easy to take out in photoshop should I need to. 6mm ply would probably work as well and be lighter to move around, though it was more expensive than the MDF I bought. Also the MDF will take screws better for heavier works. OSB might do, but the surface is rough as hell.
The reason for a free-standing panel is that I don't have anywhere with a sufficiently large clear white wall to photograph bigger work. I wanted something I could build when needed, and take apart for storage. Particularly large work will need special attention, but this will be perfect for most of my needs.