I have a task to edit exif tags and add to them application specific values.
if the exif tags exist libexif is more than happy to edit them .
but if the exif tags don't exist, i will have to create them and append them to file.
libexif uses the C fopen so i don't think there is going to be an easy way without some IO manipulation.
I am thinking to read the raw image data put them in memory , fopen(newfile, 'w')
add the exif data
and then append the image data.
only if someone knows an easier way , ( i am restricted with libexif, libexiv2 might create a liscence conflict) .
for the common good i am going to answer my own question, exif application has a modified libjpeg that enable the manipulation of the jpeg raw data. it has functions like
jpeg_data_load_data (JPEGData *data, const unsigned char *d,unsigned int size);
and
jpeg_data_set_exif_data(myJPEGImage,exif); jpeg_data_save_file(myJPEGImage,"gangrene1.jpg");
That can be used, also free available programs like imagemagick have their own libjpeg , libexif implementation to do manipulate exif and jpeg data. Hopes this helps