As it is known copy-pasting code is bad practice, I did the same mistake.

I finally found the mistake and changed:

fwrite(&buffer, 1, block_size, card);

with:

fwrite(&buffer, 1, block_size, jpg);

and the empty file problem was resolved. It was a silly mistake.

Also looks like the missing block is not actually missing. I have 50 complete JPGs.

As it is known copy-pasting code is bad practice, I did the same mistake.

I finally found the mistake and changed:

fwrite(&buffer, 1, block_size, card);

with:

fwrite(&buffer, 1, block_size, jpg);

and the empty file problem was resolved. It was a silly mistake.

Also looks like the missing block is not actually missing. I have 50 complete JPGs and it passes check50.