It would appear to be a B&O 5300 4-6-2, shined to the 9s. Unclear if the men are officials or, as the seller says, engineers in their Sunday best. Just a nice old photo.

http://cgi.ebay.com/Vintage-1920s-Railr ... otohosting

Hello,
A stunning picture, and believe it to be during the delievery of what appears to be one of the President class pacifics. Notice on the air reservoir " BLW Tested" and a date of what seems to be 3-?-27. Also, every aspect of the machinery is in as new condition. The men pictured are almost certainly officals involved with the development and/or acqisition of the engine. It must have been a grand day!
Thank you for sharing this picture.
Respectfully,
Dave Griner
arizonamechanicalengineering.com