Although there's no way to keep history states and snapshots after you close a document, you can keep a record of what you did, and it's called the history log. The history log is text that records your edits, but you can only read it. You can't play it back or reload it. You can use the history log to track your edits down to the settings you used in dialog boxes, and you can use that to manually reproduce the edits made to the file.
The history log was originally added to Photoshop so that judges and juries in court cases could have a precise record of how a digital photo presented in court as evidence differs from the original photo (for example, if a crime scene photo was brightened for clarity). If you set up the history log in a way that's appropriate for your work, it can be a valuable tool for documenting and analyzing your own processes and techniques.
If you want to keep a history log, enable the History Log checkbox in the General panel of the Preferences dialog box (Figure 14.9). You can choose whether you want to save a log with each file (select Metadata) or maintain a central log for all files (Text File). You can also use the Edit Log Items pop-up menu to set the level of detail for the log.
Figure 14.9. Enable and customize the history log in the General panel of the Preferences dialog box.
Keep in mind that if you increase the history log's level of detail, the history log can record minutiae like the folder paths and names of files you open, and the text you enter on text layers. If you choose to store the history log in metadata, it travels wherever the image travels. For example, if you type "My Stupid Boss" on a text layer because you're just playing around, and then you delete the text, the original text entry is still in the log. If you store the log in the image metadata, and your boss views the file in Adobe Bridge which can display the metadata, your boss may come across the log entry containing that text. If you or your organization has an interest in restricting certain information, you may not want detailed editing records to travel with the file. You might limit the level of detail or choose to store the log in a text file on your own machine, rather than keeping the log in the file's metadata.