First of all, it is important to realize that you do not need a high frames per second to take great screenshots, so try to maximize the settings.
With that being said, here are the settings I use when taking 4K resolution screens[i.imgur.com]. The most important setting here is "Display Mode - Fullscreen Windowed", which will be explained later.

If you have a 4K monitor, awesome! You can skip this section
For everyone else, here is the rundown on getting 4K resolution no matter what your monitor is.

STEP 1 - Open Nvidia Control Panel
STEP 2 - Go to "Manage 3D Settings"
STEP 3 - Turn DSR Factors to "4.00x (native resolution) & Apply[i.imgur.com]
STEP 4 - Go to "Change Resolution"
STEP 5 - Select 3840x2160 & Apply
From /u/the_only_luke's guide here

Even though my Nvidia settings doesn't have the DSR Factors[i.imgur.com], you can create a custom resolution under
Display>Change Resolution>Customize[i.imgur.com], and add it yourself.
This may wear down the monitor after extended use, so use it sparingly. That being said, I never came across any problems. If your monitor does not work with the 4K resolution, make sure to reduce the refresh rate (instead of 60 on my 1080p monitor, I use 30 when I upscale to 4K). This does not work for everyone!

Apparently AMD has a similar method of VSR as NVIDIA has, but I cannot test it for obvious reasons.
Here[forums.guru3d.com] is a guide I did find and has worked for AMD owners

Originally posted by Xant0r:

For users with old or non supported cards (amd for example), there is a 3rd party program to downscale 4-8K res to a 1080p monitor. Good thing is that it has an option to take screenshots at the rendered resolution, which means you can make 4-8K screens on pretty much any card that can do 4K+ res. I have been using it myself since AMD VSR is not supported for my card yet (R9 280X).
You can get it here: http://blog.metaclassofnil.com/?page_id=582 You might have to play around with the mouse settings in the config that comes with it, since the default config was not working for me mouse wise (spinning in-game).
Note that making 8K res screenshots makes extremely large screens in terms of size. They look great, but for trading you should always include normal 1080p screens and optional 4-8K screens, since not everyone has good internet and it could turn away potential interested traders that have no patience for loading a screenshot :-)

Thanks /u/Xant0r

First of all, get 4K resolution on your monitor, and launch CSGO with the settings I described above. If it looks like this[i.imgur.com] (your mouse is small, text under "News" is very small), congrats! You now have 4K!
Go to > Play > Offline with Bots, choose your map to do 4K screenshots on, choose the gametype as "Deathmatch" and click "No Bots".
Once you are in the game, make sure your developer console is turned on by pressing tilde or "~". If nothing happens, open Settings > Game Settings > Enable Developer Console "Yes".

This is where the secrets come out.

In the console type:
Then, find somewhere on the map where you like how the playside, and backside of the knife looks (make sure it is not too overexposed or underexposed.
Then, without moving a muscle, in the console type the following with an enter after each item:
You should then not have any weapon visible and you should not have any HUD.
Press 'Prt Sc' on your keyboard in order to copy the entire display. Alt-tab out of the game and open up paint, and then press 'ctrl-v' in order to paste what you copied. If you just get your desktop background, then your game was not set on windowed-fullscreen. However, if you get the ingame screenshot without any weapon and HUD, you are golden! Save this picture as a .png with a recognizable name in paint (this will be the background of the weapon).
Here is an example of what you should get[i.imgur.com]Type the following in console with an enter after each item to get back to see the weapon again:

Now, you need to take a screenshot of only the weapon. I do not know an easy way to do this, but I know how to make it easier.
Type the following in console with an enter after each item:
If your screen flashes random colors, with very little background and no skybox, you are doing great! Press 'Prt Sc' on your keyboard in order to copy the entire display. Alt tab back to paint and press 'ctrl-z' in order to undo the last copypasting, and then press 'ctrl-v' to repaste the new image (with the random colors). Save this with a different name.
Here is an example of what you should get[i.imgur.com]
If you are only doing a weapon, you are done! If you want to show the backside of the knife as well, continue to step 3.

Without moving (you should remain still during this entire process in order to make sure the screens are taken in the same light), type in:
Your knife should now be in your left hand. Press 'F' on your keyboard to inspect the knife and then snap another pic with 'Prt Sc'. As we did before, undo the last copy and paste in paint with 'ctrl-z' and repaste the new image with 'ctrl-v'. Save this with a different name.
Here is an example of what you should get[i.imgur.com]

Open the three images you created in Photoshop (I use Photoshop CC, so these directions may be different for you).

Start with one of the knife/weapon pictures, and use the quick selection tool[www.safaribooksonline.com] to select only the hand and the knife. This is the most time-consuming part of this entire section as it sometimes is really accurate and other times it is absolutely horrible. Thus, it takes a lot of time selecting, deleting, and reselecting what you want. If you have very small sections you want to select, it is easier to use the lasso tool[updateox.com] to select them.
Once you are done with your selection, click 'Refine Edge' and create a new layer (I think you can create a new layer without the refine edge tool). Duplicate that layer onto the background layer.

Repeat this process with the second picture (only if it is a knife, as you don't need two guns on a screenshot).

You should now have a picture with three layers (or two if only a weapon): one with the background, one with the playside of the knife, and one with the backside of the knife. Choose the layer with the background, go to filters, blur, and then lens blur. Play with the settings until you find something you like. Then click 'OK'. Now, the background should be blurred with two knives.
Then, if you want, you can add saturation and vibrance to the entire image using the 'adjustments' panel.
Finally, you should have something like this.[i.imgur.com]

Congratulations, you are done with the hard part!

There are several websites where you can upload your screenshots. I only use Imgur[imgur.com].


That's all folks, feel free to go to the original post on Reddit, and say thanks to the creator of this great guide, /u/Asofnowyoudie