There's other factors in play with regard to phone encryption which can complicate this process. Once you've secured that dump, you can scan it with recovery software and see if files are recoverable. This can be done in a variety of ways, such as dumping to an SD card through the recovery menu (if it allows it), and by using ADB command from the Android Development kit on your desktop. Now, IF there were recoverable files or fragments on that phone, the only way you'd be able to exctract them would be by dumping a full image of the user data partition on that phone to a computer. The longer a phone is online, the less of a chance you can recover anything. If you download large files or record videos, those files may be written to where those deleted files were, destroying them permanently. The bad thing is with a phone, it's constantly writing and overwriting data.

The only deletion that's truly permanent is a secure delete, which goes ahead and overwrites the file after it's deleted. They inspect the 'free space', and see where files marked for deletion reside, and extract them. That's how data recovery software can retrieve the files. It just marks the deleted files as OK to overwrite.

Even if you 'permanently' delete it, it's still on disk. When you delete a file, it does not actually delete the file.

Deleted pictures android recovery