This image was widely printed on lithographed postcards, so it was probably licensed from Frank Nowell, the official fair photographer of the Alaska Yukon Pacific Exposition. Apparently Otto printed it on contract for the American Post Card Co.
Otto also printed it under his own name, as Image X5 (image courtesy of Dan Kerlee):
One of the lithographed versions is shown below:
There is also an Image 42 (42 - American Bank Bldg. Seattle) showing a bank building in downtown Seattle. Reuse of image numbers and different image series make it difficult to know how many images Otto published.