Gene Robertson photo
 

I just bought this on eBay but wanted some opinions. Described as circa 1929 original and on cardboard backing. What distributors or photographers employed this backing? Anybody shed some light?

That backing would have been applied by a newspaper /archive/collector after the fact and the photographer did not do that. If that cardboard backing was removed you are most likely going to find an American League Service Bureau or Thorne photographer mark on a thin photograph.

Robertson
 

Thorne did Yankee spring training photos for about 13 years, but when the AL Service Bureau used his prints, they always looked like copies of the original prints. Thorne's 8x10s are much sharper.
Whenever I see the cardboard backing on these photos, I think Norman Paulson.
lumberjack

If its original-- and I'm not saying I think it is not, because it appears vintage--, it would likely be the newspaper or magazine that got the photo and not the photographer that put the backing on it.

I notice it says U-U on back, which brings to mind Underwood-Underwood.

That is an interesting clue. Not sure tho I want to try and separate it to check reverse of photo