Which version of Daum was this where you had the problem?
Is it related to the problem here -- Bugs in ykhwong build
Does the same thing happen in the 2014 version?

Daum is broken. Use a different build.

@skitters
This doesn't happen with 2014 version. Only with 2015 (both) builds.
And yes it seems the issues are the same. Sorry for double posting.

@collector
Thanks. For now I stick with 2014 build.
Do you might know any other DosBox fork that offers similar to Daum functionality? Basically I just want to have an ability to use that nice CRT shader.
I've tried to use libretro fork but it is not as user-friends as Daum version. I could not figure out how actually I can run any program with my configuration.

Doublescan probably just resizes the image. CRT shader then has more pixels to work with and produces a nicer image.
You could probably get the same effect with setting a scaler (normal2x or hardware2x) or larger window/fullresolution.

Actually I use hardware2x+ in all cases.

According to conf description from Daum build DoubleScan does something more than just simple resize.

# doublescan: If set, doublescanned output emits two scanlines for each source line, in the
# same manner as the actual VGA output (320x200 is rendered as 640x400 for example).
# If clear, doublescanned output is rendered at the native source resolution (320x200 as 320x200).
# This affects the raster PRIOR to the software or hardware scalers. Choose wisely.

And as you may may notice the picture looks better without DoubleScan. So shader actually works with native 320x200 resolution. Of course it's a matter of personal taste but at least the effect of the shader is more visible without DoubleScan. With it the effect of the CRT shader is barely visible: no phosphor glow and jaggies smoothing.

Hey, I found the easy way to fix Kyrandia image without DoubleScan option.
Just put 4:3 resolution of your monitor in the Fullscreen option and don't use any scales.

For me it looks like this:
fullresolution=1600x1200
scaler=none

UPDATE:
Sorry my bad. It's been a while since I've been played around with DosBox.
It looks that a true fix for the issue is to use DosBox_Daum_20140127 build.
But the settings above help Fullscreen mode to work properly. Sometimes a picture is rendered with overscan even if it's set to 0.