public class UriWrapper : Freezable
    {
        public Uri Source { set; get; }

        protected override Freezable CreateInstanceCore()
        {
            return new UriWrapper();
        }
    }

    public class UriCollection : ObservableCollection<UriWrapper> {}

    public class Test
    {
        private readonly UriCollection _imageCollection;

        public Test(UriCollection imagecollection)
        {
            _imageCollection = imagecollection;
        }

        public BitmapImage GetImage()
        {
            return _imageCollection.Count > 0 ? new BitmapImage(_imageCollection[DpiImageSource.Index].Source) : null;
        }
    }

    [ContentProperty(nameof(Images))]
    public class DpiImageSource : ObjectDataProvider
    {
        public static int Index = 1;
        public UriCollection Images { get; } = new UriCollection();

        public DpiImageSource()
        {
            ObjectInstance = new Test(Images);
            MethodName = "GetImage";
        }

    }

<Window>
    <Window.Resources>
        <local:DpiImageSource x:Key="DpiImageSource">
            <local:UriWrapper Source="1.jpg"/>
            <local:UriWrapper Source="2.png"/>
            <local:UriWrapper Source="3.jpg"/>
        </local:DpiImageSource>

    </Window.Resources>
    <Grid>
        <Border BorderThickness="1" BorderBrush="Gray" Margin="10" Padding="10"
                Background="LightGray">
            <Image  Source="{Binding Source={StaticResource DpiImageSource}}"/>
        </Border>
    </Grid>
</Window>