LÖVE

"icon.png" is a 16x16px image.
When i run the the program i get this error:

"main.lua:1: The size of the raw byte string must match the ImageData's actual size in bytes."

Is there something wrong on the script?

Check all the variants the documentation of newImageData. Note that none of the forms accepts a size followed by a filename. The closest is newImageData(filename), which doesn't need the size because it's encoded in the file itself.

Yes, the three-argument version of newImageData accepts raw imagedata as the third argument.
In your case, you want the one-argument version, which accepts a filename.

But i need an ImageData for setting an Icon. Am i right?

Yes.

In my first version of the post I asked if you were sure that you needed newImageData rather than newImage. Then I realized it was actually for an icon, not for drawing it yourself, so I deleted that part because for an icon, you need newImageData indeed.

Ok!
How could i do that? Is there a way to convert pixels to bytes and find the dimensions?

You can load an ImageData from a file like: local data = love.image.newImageData("icon.png")