#!/bin/sh
prefix="myScreen"
while true
do
   scrot -d 3 -u "${prefix}_$(date +%y%m%d_%H%M%S)".png
done

                                                                                                                         
Usage : scrot [OPTIONS]… [FILE]
Where FILE is the target file for the screenshot.
If FILE is not specified, a date-stamped file will be dropped in the
current directory.
See man scrot for more details
-h, –help display this help and exit
-v, –version output version information and exit
-b, –border When selecting a window, grab wm border too
-c, –count show a countdown before taking the shot
-d, –delay NUM wait NUM seconds before taking a shot
-e, –exec APP run APP on the resulting screenshot
-q, –quality NUM Image quality (1-100) high value means high size, low compression. Default: 75. For lossless compression formats, like png,
low quality means high compression.
-m, –multidisp For multiple heads, grab shot from each
and join them together.
-s, –select interactively choose a window or rectangle with the mouse
-u, –focused use the currently focused window
-t, –thumb NUM generate thumbnail too. NUM is the percentage of the original size for the thumbnail to be, or the geometry in percent, e.g. 50×60 or 80×20.
-z, –silent Prevent beeping

SPECIAL STRINGS
Both the –exec and filename parameters can take format specifiers
that are expanded by scrot when encountered.
There are two types of format specifier. Characters preceded by a ‘%’
are interpreted by strftime(2). See man strftime for examples.
These options may be used to refer to the current date and time.
The second kind are internal to scrot and are prefixed by ‘$’
The following specifiers are recognised:
$f image path/filename (ignored when used in the filename)
$m thumbnail path/filename
$n image name (ignored when used in the filename)
$s image size (bytes) (ignored when used in the filename)
$p image pixel size
$w image width
$h image height
$t image format
$$ prints a literal ‘$’
\n prints a newline (ignored when used in the filename)
Example:
scrot ‘%Y-%m-%d_$wx$h_scrot.png’ -e ‘mv $f ~/images/shots/’
Creates a file called something like 2000-10-30_2560x1024_scrot.png
and moves it to your images directory.