And about verification, well sometimes offices arrange verification for months, for example, they ask for different documents, may ask for these documents to be notarized. and may ask for such documents at some time during the months.
They may also ask for different photos. To reject the quality of the photo, even if it is of good quality.
Casinos have their Terms of service to request users do advanced KYC for big win, suspicious withdrawal request or after detecting activities that are intolerable by their casino rules.
Quality of photo for KYC is important but it's not all. You must make photos which fulfill requirement from the casino so must provide exactly what they want. In addition, documents must be from yourself, not faked or stolen documents from someone else.
Legit casinos will do approve KYC documents for their users if their Compliance team or a third party KYC service provider conclude that documents are legit and valid.
To prevent the KYC process from being requested a Second time, many things have to be done, first the documents that are sent must be legible and, as you say, the photo must be in high quality so that it can be processed, as far as I'm concerned. I understand that the kyc Process must be done quickly so that it can be approved quickly, in other casinos it takes a long time for them to be approved, this is something that those who want to Undergo a kyc process should take into Consideration, that's why it is necessary to review everything and that they are safe.