Hola Shirley, 

This is the way I read this passage and it may help you to read it differently:

"Gracias a que le dí la vuelta..."= Thanks to the fact that I turned it over (turned the photo over)

"...ví que tenía escrito lo siguiente:" =  I saw that it had written (on it) the following:

Tener- tenía= it had (written on it) was used in the imperfect to describe the condition of the photo. 

For now I hope this helps a little. Inma will no doubt add to this with a better explanation than I can give.

Clara 

P.S. After a search through the lessons in Kwiziq, this answers your query Shirley:

Using tener + past participle to express the completion of an action (perífrasis verbal)