Znojmo, Czech Republic

The submitter states:

My father took this photo on April 1, 2010, through his windshield, while driving through Znojmo, Czech Republich.

He didn't notice the white object above the building on the left side, until he watched the photo on the computer.

It doesn't look like spot on the windshield, but we are not sure, because it seems to be illuminated by the sun. Maybe you can say what it could be.

Thanks

Alex