BERGNER family in photo album has been found!
Thanks to the improved census indexes at Ancestry.com, I managed to find the right BERGNER family a couple of months ago, and I should posted then. The family in the album is that of Louis and Augusta BERGNER, who immigrated in the late 1860s from what is now Germany and landed in New York City. They were settled in Wisconsin by 1870 (mainly in Shawano Co.). They enjoyed a prosperous life, with business interests in lumber and grain. In the early 1900s, as I learned eventually, some members of the family relocated in Everett, Washington. That's where the album was found, in the attic of a big old house in Everett.
The 1930 census index showed several young BERGNER children in Shawano Co., and by using an online phone directory I was able to speak to one of those children. It turned out that he had a niece living very near me, and I was able to give her the album.