Problem With If Statement

[user_deleted]

I wrote script:

image test(
image obrazek=0
)

{
kolor = Color(720, 486, 1, 0, red, red, 1, 0);

if (obrazek==0) <==== Here i want check are input is connected to something or not.
{
return kolor;
}
else
{
return obrazek;
}
}

And got error.

How I can check information are picture is connected to input or not?