The signature on the girl would be her given name "miyiko" みゐこ. "Yi" is a romaji for ゐ which is usually not used in modern Japanese.
The name of the photo studio is 高木寫(=写)真店 Takagi Photo Studio.
The one on the back would be 芝川実 Shibakawa Minoru, or could be 寛 Hiroshi. It's a male name, anyway.