Is this truly a TRNG?
Just no.
If you use some files and a CSPRNG as data source for a deterministic algorithm, it's not a true random number generator.  

According to your own Schneier quote:  


  If you run the sequence generator twice with the exact same input (at
  least as exact as humanly possible), you will get two completely
  unrelated random sequences.


It sounds like your generator will generate the same numbers, so... don't mistake the CSPRNG for your generator. The CSPRNG is input for your generator. (And even if not, same input for CSPRNG is same output).   

There are other problems (like thinking two images of the same place are independent), but they don't really matter anymore.  

...  


  Obviously I tried to create a TRNG


That's a pretty good giveaway that you don't really know what your doing. A TRNG can't be created with some software piece on a turing-machine-alike. Nobody can, never.