Unfortunately, the link to the web where I bought the camera seems to be broken... Anyway, I attach you every single file I've got about the camera and the SD library, where you can find all the source codes and sample codes. The most relevant sample code can be found at ./JPEGCamera/examples/JPEG_Sample/JPEG_Sample.pde. I must admit that I tried to jump into the source codes of both the camera and the card, and I found out that, for the writing, they both use a function called write (obviously overloaded, not the same for both), whose source code is also available on the .zip file I attached to you, but it's too complicated to me to understand 
I thank you the efforts you're doing to help me.
JPEG Camera Libraries.zip (94.2 KB)