A credit card number is partially obscured by a stain. Deduce the structure of the obscured digits and determine their readability.

The full PIN visible on the upper part of the card is 0691-1702-4355-7630. This is a 16-digit PIN, formatted in four groups of four digits.

From the crops, the following parts of the lower PIN are discernible:

• The first two digits are 07.
• A middle section of four digits is 0157.
• The last two digits are 99.

The lower PIN can be represented as: 07XX-XXXX-0157-XX99.

The stain covers:

• The 3rd and 4th digits of the first group (2 digits).
• All 4 digits of the second group (4 digits).
• The 1st and 2nd digits of the fourth group (2 digits). In total, $2 + 4 + 2 = 8$ digits are covered by the stain.

Despite the multiple crops provided to enhance visibility, the black stain remains completely opaque over the affected areas. No digits, partial digits, or outlines are discernible underneath the stain in any of the images.

The digits covered by the stain are unreadable.