Good luck with your application.......this is the most important thing and step....
1) Photos : Print in good paper(glossy something) 2-3 a page with description(user micrsoft word) next to it will work. DONT FORGET TO TAG EVERYONE IN IT. it is not how many pictures you send, it is how good the pictures are, what is in it, the descrition. If it is a temple/religious wedding, put in as many rituals as possible. Show parents, in laws, sibilings, immediate family memebers. how many peoople attended the wedding. give as many as possible, if you have a reception at the end of it, add as many photos of it......if court wedding, then evidence of the same.....they have to look at the pictures and other documents to determine that marriage is geunine, so dont leave anything to guesses...parents, in laws and sibilings at the wedding is kind of must, if they are not there, it would be good if you can write a cover letter to explain why they were not there, for eg, father had a health codition, hence could not attend....etc...if love marriage, explain your situation etc.
2) copy of Boarding passes along with tictets showing iternary is good enof...
3)copy of letters written between the couples is also fine...you have hand written letters....wow!!!
4)if you have left over INVITATION put ORIGINAL ones. If you dont, then take copies and give them.
5) continued relationship is what they look for, so if you say you know your spouse from 1 year, they need to see proof of communication between you for one year. Any meetings you had, any receipts of going to anywhere together! Phone logs, chat logs, whatzapp, Viber, Skype anytin...print and add it.....if you bought him/her gifts, then add pics of those, recepits etc....any trips you went, pictures of those,
6) copy of wedding certificate - registered one is must, temple one or any other one you have....
When you say scan what dooes that mean? if you scan, you need to print it out and put it as part of the application......As much as possible, be sensible about getting good quality paper and prints.....
Many times, once the process is complete NDVO returns photos and documents back.....but to be double sure - take copies you will need it.