SerJook

use \lsolesen\pel\PelJpeg;
use \lsolesen\pel\PelTag;

$jpeg = new PelJpeg("test.jpg");
$ifd0 = $jpeg->getExif()->getTiff()->getIfd();
$entry = $ifd0->getEntry(PelTag::SOFTWARE);
if ($entry !== null){
    $entry->setValue('Edited by PEL');
}
$jpeg->saveFile("test_out.jpg");