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Filename : photographer.c
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/*
 * libexif example program to display the contents of a number of specific
 * EXIF and MakerNote tags. The tags selected are those that may aid in
 * identification of the photographer who took the image.
 *
 * Placed into the public domain by Dan Fandrich
 */

#include <stdio.h>
#include <string.h>
#include <libexif/exif-data.h>

/* Remove spaces on the right of the string */
static void trim_spaces(char *buf)
{
    char *s = buf-1;
    for (; *buf; ++buf) {
        if (*buf != ' ')
            s = buf;
    }
    *++s = 0; /* nul terminate the string on the first of the final spaces */
}

/* Show the tag name and contents if the tag exists */
static void show_tag(ExifData *d, ExifIfd ifd, ExifTag tag)
{
    /* See if this tag exists */
    ExifEntry *entry = exif_content_get_entry(d->ifd[ifd],tag);
    if (entry) {
        char buf[1024];

        /* Get the contents of the tag in human-readable form */
        exif_entry_get_value(entry, buf, sizeof(buf));

        /* Don't bother printing it if it's entirely blank */
        trim_spaces(buf);
        if (*buf) {
            printf("%s: %s\n", exif_tag_get_name_in_ifd(tag,ifd), buf);
        }
    }
}

/* Show the given MakerNote tag if it exists */
static void show_mnote_tag(ExifData *d, unsigned tag)
{
    ExifMnoteData *mn = exif_data_get_mnote_data(d);
    if (mn) {
        int num = exif_mnote_data_count(mn);
        int i;

        /* Loop through all MakerNote tags, searching for the desired one */
        for (i=0; i < num; ++i) {
            char buf[1024];
            if (exif_mnote_data_get_id(mn, i) == tag) {
                if (exif_mnote_data_get_value(mn, i, buf, sizeof(buf))) {
                    /* Don't bother printing it if it's entirely blank */
                    trim_spaces(buf);
                    if (*buf) {
                        printf("%s: %s\n", exif_mnote_data_get_title(mn, i),
                            buf);
                    }
                }
            }
        }
    }
}

int main(int argc, char **argv)
{
    ExifData *ed;
    ExifEntry *entry;

    if (argc < 2) {
        printf("Usage: %s image.jpg\n", argv[0]);
        printf("Displays tags potentially relating to ownership "
                "of the image.\n");
        return 1;
    }

    /* Load an ExifData object from an EXIF file */
    ed = exif_data_new_from_file(argv[1]);
    if (!ed) {
        printf("File not readable or no EXIF data in file %s\n", argv[1]);
        return 2;
    }

    /* Show all the tags that might contain information about the
     * photographer
     */
    show_tag(ed, EXIF_IFD_0, EXIF_TAG_ARTIST);
    show_tag(ed, EXIF_IFD_0, EXIF_TAG_XP_AUTHOR);
    show_tag(ed, EXIF_IFD_0, EXIF_TAG_COPYRIGHT);

    /* These are much less likely to be useful */
    show_tag(ed, EXIF_IFD_EXIF, EXIF_TAG_USER_COMMENT);
    show_tag(ed, EXIF_IFD_0, EXIF_TAG_IMAGE_DESCRIPTION);
    show_tag(ed, EXIF_IFD_1, EXIF_TAG_IMAGE_DESCRIPTION);

    /* A couple of MakerNote tags can contain useful data.  Read the
     * manufacturer tag to see if this image could have one of the recognized
     * MakerNote tags.
     */
    entry = exif_content_get_entry(ed->ifd[EXIF_IFD_0], EXIF_TAG_MAKE);
    if (entry) {
        char buf[64];

        /* Get the contents of the manufacturer tag as a string */
        if (exif_entry_get_value(entry, buf, sizeof(buf))) {
            trim_spaces(buf);

            if (!strcmp(buf, "Canon")) {
                show_mnote_tag(ed, 9); /* MNOTE_CANON_TAG_OWNER */

            } else if (!strcmp(buf, "Asahi Optical Co.,Ltd.") || 
                       !strcmp(buf, "PENTAX Corporation")) {
                show_mnote_tag(ed, 0x23); /* MNOTE_PENTAX2_TAG_HOMETOWN_CITY */
            }
        }
    }

    /* Free the EXIF data */
    exif_data_unref(ed);

    return 0;
}