I am a bit confused over the photo specifications for digital photo. I understand printed photo must be 50*70 mm with size of 420 x 540 pixels. However, is it the same for digital photo or it's 35*45 mm with the same size? Also, a payment receipt from the photographer is enough?
what's the confusion ?
Get the hard copy and digital photo from the studio. They'll either give it to you in a flash drive or ask you to download from their website. I suggest not editing the photos yourself as they might be rejected.
There's a section while filling the online form where they ask the location and date the the photo was taken. If you want you can add the receipt in additional documents section but not required.