TItem.cs

using ImageFilePickerSample.Common;
using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;
using Windows.UI.Xaml.Media;

namespace ImageFilePickerSample.Models
{
    public class TItem : INotifyPropertyChanged
    {
        private Guid _ID;
        public Guid ID
        {
            get { return this._ID; }
            set
            {
                if (this._ID != value)
                {
                    this._ID = value;
                    OnPropertyChanged();
                }
            }
        }

        private ImageSource _ImageItem;
        public ImageSource ImageItem
        {
            get { return _ImageItem; }
            set
            {
                if (_ImageItem != value)
                {
                    _ImageItem = value;
                    OnPropertyChanged();
                }
            }
        }

        private async Task SetImageFromFileAsync()
        {
            var picker = new Windows.Storage.Pickers.FileOpenPicker();
            picker.ViewMode = Windows.Storage.Pickers.PickerViewMode.Thumbnail;
            picker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.PicturesLibrary;
            picker.FileTypeFilter.Add(".jpg");
            picker.FileTypeFilter.Add(".jpeg");
            picker.FileTypeFilter.Add(".png");
            var file = await picker.PickSingleFileAsync();
            var imageFile = await Windows.Storage.KnownFolders.PicturesLibrary.GetFileAsync(file.Name);
            using (var stream = await imageFile.OpenReadAsync())
            {
                var bitmapImage = new Windows.UI.Xaml.Media.Imaging.BitmapImage();
                bitmapImage.SetSource(stream);
                this.ImageItem = bitmapImage;
            }
        }

        private RelayCommand _GetImageCommand;
        public RelayCommand GetImageCommand
        {
            get
            {
                if (_GetImageCommand == null)
                {
                    _GetImageCommand = new RelayCommand(async () =>
                    {
                        await this.SetImageFromFileAsync();
                    });
                }
                return _GetImageCommand;
            }
            set
            {
                _GetImageCommand = value;
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged([CallerMemberName] String propertyName = "")
        {
            this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}