Dear Mattia, Thanks for the report.
This seems to be due to a change in behaviour of the autotools. The wrapper for the executable constructed by the autotools used to add $top_builddir/lib/.libs/ to LD_LIBRARY_PATH, so gyoto could find its plug-ins from the built source tree. It does not anymore. There are easy fixes, I'll see whether some autotools package needs to be fixed or whether to work around in the gyoto build system. Kind regards, Thibaut.