This is a photo of the 1909 World's Fair held in Seattle, the Alaska Yukon Pacific Exposition. It shows the grounds of the exposition from the University of Washington (the university took over the exposition site afterward) and appears to have been taken before the fair opened. If so, it was probably taken by Frank Nowell, the official photographer of the fair. Apparently Otto printed it on contract for the American Post Card Co.
Note the white rectangle in the lower right corner; something has been crossed out.
There is also an Image 19 (19 - Old and New City Hall Seattle) showing the new Seattle City Hall. Reuse of image numbers and different image series make it difficult to know how many images Otto published.