Description:
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Two problems with the example code on the documentation page, and as a result, the code does not work:

1) The code is incomplete.  The $content variable must be written to the image file to apply the changes - that is, to write the iptc data to the image file.  The following code must be added at the end of the example:

$fp = fopen($path, "wb");
fwrite($fp, $content);
fclose($fp);

2) The $tag variable is being "substr" twice, but this should only be done once.

The existing code is this:

    $tag = substr($tag, 2);
    $data .= iptc_make_tag(2, substr($tag, 2), $string);

And should be changed to this: 

    $data .= iptc_make_tag(2, substr($tag, 2), $string);

Reproduce code:
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From manual page: function.iptcembed
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