Photos available in your iPhone's Photo Library were transferred from your computer via the iTunes sync process. You can get the file properties on your computer, but photos transferred to your iPhone are optimized for viewing on your iPhone as part of the iTunes sync process. This doesn't change the file name, but the resolution of the original photos is changed.
Thank you for your reply!
My purpose is access to "Photo Library" by iPhone API.
Because, I know several iPhone application which has own image list and the list is synced to "Photo Library".
If I take photo by iPhone native camera, the taken photo is listed up on the image list so I guess those applications can access to "Photo Library" directly.
Photos captured by your iPhone are stored in your iPhone's Camera Roll, not in your iPhone's Photo Library. Only photos transferred from your computer are stored in your iPhone's Photo Library. The Photo Library and Camera Roll are for different purposes and are separate.