[Ger-Poland-Volhynia] German Names

[JSchu9014 at aol.com]

Does anyone know if the name OLGA is considered a shortened version or nick 
name for Ottilie?  Also, is the name ELSA considered a nick name or shorted 
version for something else?  If so, what would the formal name be?
Both of these names were found on the back of an old family picture taken 
around 1891 but can find no trace of these two girls.  Any help will be 
appreciated! Thanks
Janice