int im_histlin( IMAGE *im, const char *fmt, ... );
int im_updatehist( IMAGE *out, const char *name, int argc, char *argv );
const char *im_history_get( IMAGE *im );
formats its arguments as printf(3), appends " # time-and-date", and appends
the whole line of text to the image history. The string is typically the
command-line action that would be required to do whatever it is that you've
just done to the image.
is given a standard argc/argv, formats them appropriately, and calls
im_histlin(3) for you. Note that the program name is passed separately.
returns the entire history of an image as a single C string, one action per
line. No need to free, but you mustn't modify either.
The function returns 0 on success and -1 on error.