Yes, the GFDL is a free content license if used without the invariant sections, because the nature of the GFDL is that it transfers rights fully. When something is given a GFDL license, a person can copy it, transfer it and modify it. Of course, anyone else can do the same thing, so a person would have a hard time profiting off derivative works, but it sill a derivative license.
Yes, the GFDL (GNU Free Documentation License) is a free content license when used without invariant sections. Without the invariant sections, the content is presumably okay to copy, change, or distribute it. This would include front cover texts or back cover texts. This applies to photos, texts, and other online materials.