File not found exceptions regardless of how the file is referenced

Question

I have a String to Img converter for displaying images in a DataGrid based on results of various methods that run, but for a reason I can't get my head around why my code can't find the images.

This is my converter, testing various different paths to PNGs that are all in /img/

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
    BitmapImage image = null;
    var str = value.ToString();
    //TODO Use new icons
    if (str == "pass")
    {
        image = new BitmapImage(new Uri("pack://application:,,,/img/Icon-Pass.png"));
    }
    if (str == "fail")
    {
        image = new BitmapImage(new Uri("/../img/Icon-Fail.png", UriKind.Relative));
    }
    if (str == "warning")
    {
        image = new BitmapImage(new Uri("../img/Icon-Warning.png", UriKind.Relative));
    }
    if (str == "notapplicable")
    {
        image = new BitmapImage(new Uri(@"/AppName;component/img/Icon-NonApplicable.png", UriKind.Relative));
    }
    return image;
}

My project's structure is:

AppRoot/
├─ Helpers/
│  ├─ ImgConverter.cs
├─ img/
│  ├─ Icon-Pass.png
│  ├─ Icon-Fail.png
│  ├─ Icon-Warning.png
│  ├─ Icon-NonApplicable.png

But with all of these I get a mixture of File not found, directory not found and cannot locate resource exceptions

I can only assume I'm missing something dumb obvious, but I think I'm too deep to see it.

Edit - Resolved For the pack Uris to work, the Buid action for the images must be set to "Resource". Thanks @KlausGütter :)