As written in the description, the point of this Guide is for you to learn how to add these fields to your screenshots.

Ironically enough, usually the name is written on the USERS IN THIS SCREENSHOT -field, but at the time of making this guide, it's broken.

Take a screenshot in the game.
Check its APP-ID from the Steam Store.


For example, Grand Theft Auto V is that of APP-ID 271590.

Get your Steam3ID from here: http://steamid.io and exclude the U:1: -prefix.Mine for example: [U:1:40454810]
Is thus folder: 40454810

Navigate yourself to

For me that would be

1. Inside the 760 -folder, open up screenshots.vdf
   
2. Click Select a program from a list of installed programs
   
3. Choose to open it up with WordPad.

1. Press CTRL+F to bring up the Search -feature and type in your game's APP-ID.
   
   • Grand Theft Auto V for example was APP-ID 271590
2. Press Enter.
   
3. Look for the screenshot entry you want to modify; they're displayed in
   
   YYYY-MM-DD
   EDIT: Nowadays,
   YYYYMMDDHHMMSS_x.jpg

   Year, Month, Day, Hour, Minute, Second, how manyth that second
   -standard. If you can't find it, see the "If you cannot find the entry" -part.
   
4. In between "imported" and "width" include the metadata you wish to apply.
   
   For tagging users
   "taggedusers" { "0" "SteamID64" (Refer to http://steamid.io ) "1" "SteamID64" (If more than one person) }
   
   
   For marking the location
   "location" "location"
   
   
   For naming the included Workshop content
   "taggedpublishedfiles" { "0" "Workshop Item ID (URL has it)" "1" "Workshop Item ID (URL has it)" }
   
   
5. Once you're done, hold CTRL and press S.
   
6. Launch Steam and try to upload the screenshot like you normally would and this data should be included.

If you're unsure of which one yours was, you may navigate yourself to *\760\remote\<app-ID>\screenshots\ or click View > Screenshots > (Show: Game) > Show on disk.