A 64GB iPad can hold approximately 28,000 photos. This estimate assumes that each picture is about 2 megabytes. In practice, the number that can fit depends on the size of the photo files and how much free space is available to the user.
Sizes of picture files vary depending on factors such as the camera they were taken with and the image format in which the user saves them. This makes it difficult to give a precise answer, because it depends on the specific pictures that the user is transferring onto the iPad.
The iOS mobile operating system uses a portion of the storage space on a 64GB iPad, meaning that significantly less than 64GB is available for user data storage. Any other user content, such as movies or music, also takes a portion of the space available.