Hi,
As is the reason for this post, there is a slight size difference as well as lack of XnConvert's bottom drop-shadow in XnView MP's icon:
========================================================================================
So XnView MP icon needs a same size fix so to be the same as XnConvert icon!
...So I did a bit of image editing and simply re-used the existing XnConvert icon as the base and cut out the eye neatly:

-It's now exact same dimensions and drop-shadow as XnConvert icon at 256x256.
-As you can see I added noise effect to the White 'eye' background Sclera - also the dots in the eye Sclera is added 'noise' effect for fun.
I think a background 'eye' Sclera would be better and it even shows up nice on 'black' and other darker backgrounds.
Another comparison:
existing (without background Sclera+drop shadow)
with background Sclera+drop shadow:
Here is a 16x16 comparison (click on image to enlarge):
here is the transparent 256x256 rgb white-noise-background 'Sclera':
picture.zip
Comparison of the fixed

(apng preview):
Thibaud has the original vectors to make any such proposed changes! 
You do not have the required permissions to view the files attached to this post.