Currently, no. The only file-based validation Assets fields have right now is the type. If you want to enforce a certain size, you can do that on the template end using image transforms. I would suggest adding some instruction text to your Assets field that provides a minimum suggested size, and note that smaller images will be scaled up and look gross.
That said, if you really want to enforce a minimum width/height, or other properties, you can do so by writing a plugin that provides its own field type, which extends AssetsFieldType and overrides its validate() method with your custom validation:
public function validate($value)
{
// Let AssetsFieldType do its validation first
$errors = parent::validate($value);
if (!is_array($errors))
{
$errors = array();
}
if (is_array($value) && !empty($value))
{
foreach ($value as $fileId)
{
$file = craft()->assets->getFileById($fileId);
if ($file)
{
if ($file->width < 600 || $file->height < 400)
{
$errors[] = Craft::t(
'{filename} must be at least 600x400px.',
array('filename' => $file->filename)
);
}
}
}
}
if ($errors)
{
return $errors;
}
else
{
return true;
}
}