Had issues uploading images to a prestashop install after a server upgrade.
The error message was: image format not recognized, allowed formats are: .gif, .jpg, .png
Open images.inc.php and go to about line 84 where you see this code:
// is it a picture ?
return $mime_type && in_array($mime_type, $types);
Change it to this:
$mime_type = preg_replace('/;scharset.*$/','',$mime_type);
// is it a picture ?
return $mime_type && in_array($mime_type, $types);
Doneski