Hi linsys,
You're just a bit confused there I think...
TGP = Thumbnail Gallery Post, which is a site that excepts (in most cases) thumbnail galleries built by other webmasters (for the most part anyway).
Thumbnail galleries = Photo or movies galleries which a webmaster submits to a TGP.
So you wouldn't be trading links on a thumbnail gallery but if you own a TGP site you would be...Get it?...
Regards,
SF