The validity of your marriage is being questioned by the CO. Did you marry after the notification informing you of initial selection? If you did, then your marriage may be regarded as a “pop-up” marriage; that is a marriage for the purposes of attaining an immigration visa, and not a bona fide marriage.
That’s a question only you can really answer, because only you know what you have available, but I can give you some suggestions;
• Copies of Joint Bank account statements (pre-dating selection hopefully)
• Letters addressed to your spouse with the address that you both live at, preferably with dates that pre-date the notification of selection to prove you were genuinely living together.
• Utility bills, etc. in your spouse’s names
• A copy of the Mortgage/Lease/Title Deed which may be in joint names (and preferably pre-dates entry/selection of the DVL.)
Basically anything that can aid you in proving that you have a subsisting relationship and a real marriage, not a sham marriage of convenience.
Only the CO and you know this, I can only guess that the CO was suspicious of the marriage from the very beginning and wants an interview dedicated to investigating the authenticity of your marriage, showing the photographs would be superfluous because the CO's mind was already made up. Make sure you bring those photographs to the second interview too, and any photographs your friend(s) might have that are relevant.
@slash_dot,well said.