metadata - How can I add the DateTimeOriginal property to a jpg using PEL (php exif library) -

i have been working on storing metadata in images varying success. have been able add of fields need have hit inexplicable difficulties. code works first 5 adds datetimeoriginal not being added. no errors pop not appear in resulting metadata.

function setmetadata(pelifd $ifd, array $tags) {   $ifd->addentry(new pelentryascii(peltag::xp_author, $tags['author']));   $ifd->addentry(new pelentryascii(peltag::xp_comment, $tags['comments']));   $ifd->addentry(new pelentryascii(peltag::xp_keywords, $tags['keywords']));   $ifd->addentry(new pelentryascii(peltag::xp_subject, $tags['subject']));   $ifd->addentry(new pelentryascii(peltag::xp_title, $tags['title']));   $ifd->addentry(new pelentrytime(peltag::date_time_original, $tags['datetimeoriginal'])); }