I would like to use the Dropline Etiquette icons on Debian-BR-CDD Project, but its license is not DFSG compatible. So, is very common people asking about why CCs aren't DSFG compatible. The first step to understand it is, of course, reading the DFSG and CCs. But if you want a quickly way to know about CC and DFSG, take a look at debian-legal Summary of Creative Commons 2.0 Licenses.
Anyway, I've sent a email for the Dropline author asking for a possible changing in their license to a DFSG compatible, maybe following these debian-legal recomendations:
" Authors who use or are planning to use the Attribution 2.0 license should consider a similar Free Software license such as a BSD- or MIT-style license [BSD], [MIT]."
"Authors who use or are planning to use the Attribution-ShareAlike 2.0 license should consider a similar Free Software license such as the GNU General Public License [GPL]."
Now I'm waiting...