Digital cameras and smartphones store user-created photos and videos in the DCIM folder by default; this includes photos that were saved by the user from email, MMS, etc. If the user interacts with the photo, it is commonly saved here. The exception may be third-party applications where the images are stored local to the application directory. DCIM stands for Digital Camera Images. Examining this folder provides access to all the photos the user took with the smartphone. The acquisition method determines if deleted photos are placed into the Media folder for examination.

Up until iOS 11, the format was consistently JPEG for images captured with the iOS device. iOS 11 introduced HEIC, which leverages HEIF (High Efficiency Image Format) and uses advanced compression to retain great image quality.¹

The PhotoData folder normally contains additional metadata and thumbnails for each photo. iOS 7 and iOS 8 introduced new features for photos to include Photo Stream, Moments, and Recently Deleted. Photo Stream allows the user to sync photos with multiple devices. The metadata for each file remains intact, so forensic examination allows the examiner to match the photo with the device for which it was recorded/taken. Moments allow the user to look at photos based on dates and locations and even allow searching on the device. Moments will be covered in a lab in section 4.

Recently Deleted photos was introduced with iOS 8. This was developed to allow a user to change their mind and recover photos that were recently deleted. The photos remain in this directory for ~30 days. After the ~30-day period, they are no longer recoverable to the user. This does not mean that file carving will not recover the data if the acquisition type supports it. Additionally, these deleted photos may exist in iCloud, Google cloud or elsewhere. Selfies, as previously discussed, were introduced with iOS 9. Finally, the ability to hide photos was introduced in iOS11. All of the features are available in iOS15.

Reference:

[1] https://for585.com/heic (What is HEIC?)