This command takes screenshots with the name of the current map, and separates them into files with the name of the current mode, adding a number to not replace the same image...
This script replaces only the F12 key bind, and the file directory works like this:

Screenshots/instactf/dust2-1.png

To install just add the file ss-filter.cfg in the root of your Sauerbraten, then open autoexec and type:
exec ss-filter.cfg
and save.

=)

Imgs:
https://imgur.com/a/U5kZh
https://i.imgur.com/1nlNCaH.jpg

13/02/2019
Now it's much simpler and with some new features.
- Informations about the current match will appear in the upper right corner of the screen when taking a screenshot.
- "nohud" and "editing" will be added to the name of the screenshot to be easy to filter them.

//Screenshot Filter v2 by Salatiel
//13/02/2019

tabs = "^n"
loop t 30 [
tabs = (concatword $tabs "^n")
]

screenshotfilter = [
screenshotdir ""
oldgamehud = (getalias gamehud);
if (mapname)[cmapname = $mapname][cmapname = "untitled"]
if (&& (= $editing 0) (= $arg1 1))[
minimapalpha 0.3;
gamehud = [result (format "^f4Screenshot: ^f7^"%1^f7^" ^f4/ ^f1%2 ^f4/ ^f0%3 ^f4^n^f2%5 ^f4KD:^f1%6^f4/^f1%7 ^f4server: ^f7%8 ^f4playeres: ^f7%9%4" $cmapname $getname (timeremaining 1) $tabs (at $modenames (getmode)) (getfrags) (getdeaths) $connectname (listlen (listclients 1)))]
]

sleep 100 [
screenshot (format "SCREENSHOTS/%1/%2-%5%6%3%4" (at $modenames (getmode)) $cmapname (getmillis) (if (mapname)[result $timeremaining][result (rnd 100)]) (if ($hidehud)[result "nohud-"][result ""]) (if ($editing)[result "editing-"][result ""]))
gamehud = $oldgamehud;
minimapalpha 1;
]
]

bind f12 [screenshotfilter 1]