As Pix4Dmapper use Exiv2 and it distributed under GNU General Public License, version 2. I request Pix4Dmapper source code. You must provide source code or you volatile GNU General Public License.
You are correct, Pix4Dmapper does use Exiv2.
However, you should be aware that we have no obligation to release Pix4Dmapper source because we licensed Exiv2 for commercial use from the copyright holder of Exiv2. Our license is for perpetual commercial use of all current and future versions of Exiv2.
This dual-license structure is common in GPL software and should be familiar to most open source aware individuals. An example can be seen on the MySQL licensing page here: MySQL :: Commercial License for OEMs, ISVs and VARs
Let me know if you have any further questions or requests.