Regarding the source for the Rabbeinu Tam saying that its better for a woman to remain an Agunah her whole life rather than receive a questionable GET, although still not 100%, I think its in Rabbeinu Tam, Sefer HaYashar, Responsa, No. 24 (ed. Rosentahl, Berlin, 1898, pp. 39-42).
Otherwise you may possibly find reference to it in any of the following:
Rema, Even HaEzer 154:21
Nimukei Yosef, Yevamos 1a in the pages of the Rif s.v. Oh Nimtzeu, quoting Rabbeinu Tam
Beis Shmuel, E.H. 44:7, citing Rabbeinu Tam’s view
Aruch Hashulchan (E.H. 44:5) ruling in accordance with Rabbeinu Tam
Rabbeinu Tam’s opinion explained in the Chazon Ish E.H. 79:16
BTW regarding pictures and tznius, although I too don’t have a precise source, do agree with the guy at the Chasunah. (I’m not sure if forbidden is the right term; perhaps improper is more apt.) Why do you think the Rabbonim advised the Chareidi newspapers not to print women’s photographs? For tznius purposes. Whether you agree with it or not, he didn’t make this up.
And didn’t Sarah Umeinu hide from the guests when Avrohom Avinu invited in the three guests? Sarah Umeinu did so for tznius reasons.