Skyrim is an artistically beautiful and amazing game, and one of the best games to take epic screenshots. Fortunately, it has also useful tools allowing the player to make personalized pictures.
The first thing to know is... how to take a screenshot. The most convenient way is to use the Steam tool, as you can easily upload your pictures to your profile. To take a picture, just press F12 (default key) ingame, and a screenshot notification should appear in the corner. You can also tweak the Steam options to change the key or to have a lossless copy of your screenshot.
To use the following command, press the key under Escape and on the left of the number keys bar. It can be a ~, a ` or a ² depending on your keyboard. Then you can type your command, press enter to apply it, and press ~/² again to close the console screen.
tm (Toggle Menu) will hide all the HUD components, including menus, compass, crosshair and even the console menu (but it is still here so you will have to use it blindly after entering this command). Use tm again to show the HUD again.
tfc (Toggle Free Camera) will let you move the camera anywhere. Use your usual movement keys to move, and your left/right mouse buttons to move upward and downward. Your character will disappear if you are in first person view mode (hostiles will still attack at your initial position), but will stay if you are in third person view mode. Type tfc again to disable it.
tfc 1 Adding a '1' will also pause the game, and thus let you frame your picture peacefully. Type tfc again to disable it.
sucsm <value> (Set UFO Camera Speed Multiplier) will change the free camera speed. The value 50 will make it move 5 times faster than initially.
fov <angle> (Field of View) will change the the Field of View angle value (in degrees). Increasing the value will zoom out, decreasing it will zoom in. The default angle is 65 (which can be tweaked permanently -a lot of people like it higher when playing).
csb (Clear Screen Blood) will remove the blood on-screen effect. Useful for combat screenshots.
set gamehour to <hour> changes the time, with <hour> between 0 and 23 (e.g. "set gamehour to 15" sets the time to 3:00 PM). A superior value than 24 will also advance the day, but negative values crash the game. Nice if you want to change the lighting of the scene.
fw <formid> (Force Weather) temporarily changes the weather. Check here[elderscrolls.wikia.com] for the list of formid.
See this page[www.uesp.net] for more details about the console or more commands.
A trick that can be used to spice up your shot is to add a depth of field effect. When you press Tab (Item/Magic/Skill/Map menu), the game alters the background, but it is hidden by the menu. Just hide the menu with tm before pressing Tab, and enjoy the effect in your picture! I would not recommend to abuse of it, though.
It is obvious that your pictures will be prettier if you use higher quality graphics options. Tweaking the .ini files can also be useful to improve the graphics. The best english-written guide I've found so far is the Geforce Optimize[www.geforce.com] one, it details the effect and the performance impact of each option and give some nice advanced tweaks. Don't forget also the free official High Resolution Texture Pack to improve the textures.
Mods are also cool to add custom assets, new effects, replace textures or even tweak the graphic engine (ENBSeries[www.enbdev.com]). They can also help taking screenshots, for instance iHUD[skyrim.nexusmods.com] hides the HUD when not needed, so you don't even need to use tm anymore! (thanks cqdemal). For other mods, check the Steam Workshop and the Skyrim Nexus[skyrim.nexusmods.com].
Now you're ready to make beautiful pictures! You can post your best shots to the New, New Unofficial Screenshot thread in the Discussions section, and share your amazing adventures with other players!
I hope you will find this guide useful. Feel free to add a comment below if you think I should add some things. Also I'm not a native English speaker, so please tell me if you find any language mistake.