Since editors can add their own descriptions / alt-properties to images or pdf's that they upload to ImageVault, is it possible to fetch these and make them searchable from the regular site, as meta tags? Or are these properties only for internal use within ImageVault?
Lets say my norwegian editor wants to an image called Car 1, that is used on several other languages on the site. Is it possible to have him edit the image and in the custom field "NorwegianName" add the name for the car in norwegian, have him add the image to the page and then have the norwegian visitors be able to search for Car 1 in norwegian and have it displayed?
The media information you refer to is what we call Metadata in ImageVault.
Metadata is fully supported by the API and is very easy to retrieve, here is a code snippet on how to retrieve the value of a specific metadata called "Headline" for a media file. (this is a console application but the concept would be the same on a web page; the ID can be found on the ImageVault property)
// Load a specific media,
// make sure to include metadata.
var client = ClientFactory.GetSdkClient();
var res = client.Load<MediaItem>(1170).Include(x => x.Metadata).FirstOrDefault();
// Get a specific metadata value
var myMetadata = res.Metadata.Find(x => x.Name == "Headline");
Console.WriteLine("Headline metadata value is: " + myMetadata.Value);
You can find more examples on querying media and Metadata in the c# examples section on http://imagevault.se/doc.