I have put all the information in review.apt file.
DTED data is freely available in the GDAL Data Download area:
JP2 data and ECW data are samples generated by means of the gdal_translate utility from the originating small_world.tif file available at:
After a brief conversation on IRC between myself, Mateusz Loskot and Frank Warmerdam, I have asked if there is a disclaimer which grant that data is freely re-distributable. After my request, the GDAL team added this:
Finally MrSID data has been found here:
As stated in the note of that free data download site, I have added the required line in the review.apt file:
Data Credit: "Office of Geographic and Environmental Information (MassGIS), Commonwealth of Massachusetts Executive Office of Environmental Affairs"
Let me know if additional information are required.