Hi,

I'm going to be doing some guessing here of what your object XSXS is supposed to contain as I'm not 100% sure I understand your requirements ... I might be a bit wrong but hopefully you can pick through and amend.

You need an object in that list - a List can only contain a list of a items.

On the left hand side of your declaration for XSXS you have a list of string arrays - here each string array in the list is the item(s) in the list. On the right hand side you're trying to create a list with lots of "things" - we need this thing to be a single thing and we need both the left and right side to match! This "thing" can be a bespoke object/class where you can put all your types of strings and the like.

So you need to change

List<string[]> XSXS = new List,<string, string, string, List[]>

to:

List<XSXSItem> XSXS = new List<XSXSItem>();

or easier - we can shortcut this to

var XSXS = new List<XSXSItem>(): 

and rely on the right side to do the declaration and typesetting effectively.

Then it looks like this XSXS item can contain none-to-many image media items (this is the bit I'm slightly unsure of and you might need to redesign this object). So we have a list of copyright items and within each one we have a list of images that have a matching copyright?!

So how do we go about defining XSXSItem so you can add the attributes like copyrightUrl that you seem to need and also add an image to a variable sized list. Easy, just create a new class to store this in which also contains a list of another class.

Now I'm guessing that you're doing all this in a Razor Umbraco View and haven't quite got into creating Models, Views, Controllers and compiling code and the like .... that's fine! Let's do something for now that is not recommended for the long haul but gets you started and put the classes inside the view.

You can do this by just pasting the following at the bottom of your razor view. I know you're going to clean this up eventually and put this into it's own Model file and keep the c# purists happy but this will work for now:

@functions {
    public class XSXSItem
    {
        public XSXSItem()
        {
            // this is in the constructor of the class to "init" a new list so you can just start adding image items to the list in your code straight away
            XSXSImageItems = new List<XSXSImageItem>();
        }
        public string Copyright { get; set; }
        public string CopyrightUrl { get; set; }
        public List<XSXSImageItem> XSXSImageItems { get; set; }
    }

    public class XSXSImageItem
    {
        public string ImageUrl { get; set; }
        public int ImageId { get; set; }
        public string ImageName { get; set; }
    }
}

Right so we've now got a class where we can store your XSXS Items and their associated media items. I can't test your entire code as I don't have the libraries you have but I think you need something like:

    // get all images from media library
var allMedia = Umbraco.MediaAtRoot().DescendantsOrSelfOfType("image");

// declare list to hold xsxs media items and their children
var XSXS = new List<XSXSItem>();

//iterate through each image
foreach (var image in allMedia)
{
    //declare locals
    var imageName = image.Name;
    string copyright = "";
    string copyrightUrl = "";

    //extract metadata
    var physicalPath = Server.MapPath(image.Url);
    var directories = ImageMetadataReader.ReadMetadata(physicalPath);
    var IptcDir = directories.OfType<MetadataExtractor.Formats.Iptc.IptcDirectory>().FirstOrDefault();

    if (IptcDir != null)
    {
        var descriptor = new MetadataExtractor.Formats.Iptc.IptcDescriptor(IptcDir);
        copyright = descriptor.GetCopyrightNoticeDescription();
        copyrightUrl = descriptor.GetSourceDescription();
     }

    //iterate through XS images and check metadata against XSXS List to qualify if to be added as a unique entry or append an existing entry
    bool check = false;
    if (imageName.EndsWith("XS"))
    {
        // check if it's in the list already by using Linq to search the copyright for a match. The .FirstOrDefault is basically give me the item or Null
        var existingItem = XSXS.Where(x => x.Copyright == copyright).FirstOrDefault();

        if (existingItem == null)
        {
            var newItem = new MyXSXSItem
            {
                Copyright = copyright,
                CopyrightUrl = copyrightUrl
            };

            // add the image 
            newItem.XSXSImageItems.Add(new XSXSImageItem
            {
                ImageId = image.Id,
                ImageUrl = image.Url,
                ImageName = image.Name
            });

            // add this new item to our master XSXS list
            XSXS.Add(newItem);
        }
        else
        {
            // base item is there - just add an image to the lsit
            existingItem.XSXSImageItems.Add(new XSXSImageItem
            {
                ImageId = image.Id,
                ImageUrl = image.Url,
                ImageName = image.Name
            });
        }
    }
}