Select values (not from a table) not conntained in an SQLite table

In my Windows Phone 8.1 App I have an SQLite table in which every file contained in the folder Camera Roll is inserted after a periodic scan. I would like to understand, given the list of all the files in Camera Roll (provided from the4 OS), which one has not already been inserted in the table. I'm using the file path as unique identifier for every record, so the question is:

Is there a query to find what file paths (not contained in a table, just a strings list in memory) are not contained in the files table? Should I create a table to contain the files paths I have in memory? Should I use some temporary structure instead?

Thank you