Introduction
I used a similar mod when I was playing Skyrim LE, but that mod never got ported to Skyrim SE. Then someone else made a similar mod for SE, but it never got updated to v1.5.97 of the game. So I decided to try and make it myself.
This tool activates on the kill move event and takes a series of (hopefully really cool) screenshots. It consists of an ESL-flagged ESP plugin, some scripts, and SKSE DLL plugin. There are available three methods of taking screenshots. The default one requires only SKSE (but can be a bit slow), the other two require my DLL plugin (but are much faster). More about them below. Configuration of the mod is possible through the MCM.

Warning
When I started making this mod, I barely knew how to make a small esp plugin with, an equally small, Papyrus script. It turned out very soon that my super simple idea was not going to work and I would have to learn a bunch of new things to make it happen. When I was finishing, I had my first SKSE DLL plugin compiled and knew how to load Steam library at runtime in order to use its API (wtf). It was an adventure and I learnt as I went. I tested this mod as thoroughly as possible before publishing it, but I still consider it an alpha release. Mainly because of my lack of previous experiences with this type of programming. Backup your save if you want to try it out.

Available modes
PrintScreen mode
This one is very simple. It basically presses a bunch of times the Print Screen key for you with SKSE function Input.TapKey. It doesn't have any dependencies besides SKSE, but its main drawback is speed. Every screenshot creates a noticeable lag and, depending on other settings, it can turn your kill cam into a slideshow. It still works though, screenshots are saved without a problem. So if you can live with that stuttering, feel free to use it. Images are saved to the game's install directory (filename ScreenShot<index>.png). It's the default mode.

ENB hotkey mode
This works similar to the PrintScreen mode, but requires my DLL to work. ENB wouldn't register the hotkey when it was invoked with SKSE function. So I had to create the key press event on lower level, in C++. The lowest value for time interval between screenshots in this mode is 1 second, because ENB creates image files with names based on current date and time with precision to the second. It's much faster than the PrintScreen method, shouldn't cause any stuttering. You need to provide your ENB Screenshot hotkey in the MCM (Insert by default). Images are saved to the game's install directory (filename enb<date><time>.bmp). It requires ENB, of course. Otherwise the hotkey press won't trigger anything.

Steam overlay mode
This one is arguably the most interesting, because it doesn't simulate any key presses. Instead the DLL plugin loads steam_api64.dll at runtime and uses Steam API directly to trigger screenshots. This method is very fast and your screenshots are instantly visible in Steam, easy to share. But it took me the longest time to get working and the implementation feels rather experimental to me. It never failed to work on my machine, but I can't guarantee anything. I've built in a lot of checks and validation into the mod, so if loading the library won't be successful (or some other problems happen), you should immediately receive a notification. This method requires Steam overlay to be on, of course. Your screenshot hotkey set in Steam doesn't matter.

Additional configuration
Additional settings available in the MCM:

• Toggle the entire mod - allows turning mod off and on. Uncheck it and save if you plan to uninstall the mod. If you turn it off and then on again, it will reset all MCM settings to default.
• Pause the mod - allows temporarily pausing the mod. The settings won't get reset after unpausing.
• Test current settings - allows testing current settings without the need to trigger the kill cam. After checking it and exiting the MCM, the script will make 3 test screenshots.
• Start delay - you can delay the first screenshot up to 2 seconds. Will result in less screenshots per series.
• Time interval - how much time passes between each screenshot. Minimum depends on the mode: 0.5 for PrintScreen, 1.0 for ENB (reason explained above), and 0.15 for Steam overlay.
• ENB hotkey (only in ENB mode) - you need to set the same hotkey as in your ENB config. The modifier key set in ENB doesn't matter, it's not used for screenshots. There are limitations to supported keys. You have a lot of possible keys to set in ENB config, my mod supports most of them but not all. You can see more info in the screenshots of config menu. (You'll get a notification if you try to map an unsupported key.)
  

If you'd like to remove blur from kill moves, I can recommend this mod: Killcam blur removal.

Installing
With your mod manager. Remember to backup your save before installing, just in case.

Uninstalling
I did my best to provide a clean way of uninstalling and tested it on both light and heavy load order.

• Turn the mod off in the MCM. It will stop the quest and unregister for events.
• Make a full save.
• Deactivate the mod.
• Load the save from step 2. You will get notification about a missing esp, that is normal.
• Everything should be ok, make a clean save.
  

Updating
I highly encourage you to make a backup of your save. I tested the mod extensively but different things can happen on different setups. Better safe than sorry.
Simply overwrite old version with the current one. 


FAQ
I have found some awful bug./ Nothing works for me.
Like I mentioned, I tested it extensively but there are many possible setups and I can't account for all of them. Please go back to your backed up save and make a bug report. I will do my best to fix it.

I have found something weird/ wonky/ funny in the config menu.
This was my first time making the MCM. It's possible I have missed something. Please make a bug report, I'll try to fix it ASAP.

Why are you restricting supported keys for ENB hotkey? My hotkey is not supported!
There is some fuckery going on behind the scenes with converting DXScanCodes to virtual keys. I had a lot of problem with this so I made my own mapping of the certain subset of keys. In my opinion the available keys are enough, but if you really care about your key being included, let me know in the comments.


Known issues

• Mapping Print Screen in the MCM for the ENB mode will result in the key being shown as Num/. I have no idea why it happens, seems to only happen with this key. It still works though.
• Info from mods like floating health bars and floating damage will be visible on the screenshots. It doesn't get hidden like the rest of the HUD. Not sure if there's anything that can be done to fix this. Should be fixed in the v1.1.1alpha update.
• You probably will have to tinker with timing settings a bit to get some cool screenshots. Sometimes they can come out blurry/ not that interesting. I still like it though.
• There's no straightforward OnKillMove event in Papyrus. My workaround is to register for player camera change event and make checks on that event. My mod activates if the camera state is 2 which technically is VATS, but in Skyrim that's basically the kill cam. I also make check with the Player.IsInKillMove() method. If either of those 2 is true, the script fires. With this mixture of checks I was able to catch standard sword/axe/ whatever kill cam, first person kill cam and dual casting spells kill cam. But there still could be some type of kill move that will slip through.
• Regarding the 4th point above: implemented detection of kill moves could turn out too sensitive - so far I have one report of a situation when the mod would detect a kill move during combat when there isn't one. Details of this issue can be found in the Bugs tab. The v1.1.2alpha update attempts to remedy this and also provide an easy kill switch if something gets stuck: screenshots session is immediately ended if the player sheathes their weapons (details also in the changelog). This issue is still being looked at. Many thanks to IsharaMeradin for help with testing the mod and providing helpful feedback.
  

Log
If you have troubles with ENB or Steam overlay mode, it might be useful to check the DLL plugin's log. It's saved to My Games\Skyrim Special Edition\SKSE directory (AutoScreenshotPlugin.log). If the plugin's log completely empty, it means it didn't even load.

If you decided to try this mod out and got some nice screenshots, feel free to upload them here :). I'd love to see them.


Here's a list of sources that helped me immensely in making this mod:

• SKSE Plugin Creation article on the Creation Kit Wiki
• SKSE Plugin Creation tutorial on GitHub - from here I could download VS project with an example plugin
• CommonLibSSE on GitHub
• MCM Quickstart on GitHub
• r/skyrimmods on reddit
• r/skyrimmods on reddit again
• Steamworks API Overview
• Download Steamworks SDK (you can login with Steam Store credentials)