def valid_dimensions
if file.path[-3,3] == 'swf'
header = SwfFile::FlashFile.header file.path
width = header.width
height = header.height
else
dimensions = ImageSize.path(file.path).size
width = dimensions[0]
height = dimensions[1]
end
unless (width == 600 && height == 200) || (width == 300 && height == 250) || (width == 468 && height == 60) || (width == 728 && height == 90) || (width == 160 && height == 600 || (width == 240 && height == 400))
errors.add :base, "error"
end
end