public void SetCompressionQuality( 
   int quality
)

QueuedTask.Run(() =>
{
  //Open the raster dataset on disk and create a compressed raster value dataset object
  var dataStore = new ArcGIS.Core.Data.FileSystemDatastore(new ArcGIS.Core.Data.FileSystemConnectionPath(new System.Uri(@"e:\temp"), ArcGIS.Core.Data.FileSystemDatastoreType.Raster));
  using (var fileRasterDataset = dataStore.OpenDataset<ArcGIS.Core.Data.Raster.RasterDataset>("Hydrant.jpg"))
  {
    var storageDef = new ArcGIS.Core.Data.Raster.RasterStorageDef();
    storageDef.SetCompressionType(ArcGIS.Core.Data.Raster.RasterCompressionType.JPEG);
    storageDef.SetCompressionQuality(90);

    var rv = new ArcGIS.Core.Data.Raster.RasterValue();
    rv.SetRasterDataset(fileRasterDataset);
    rv.SetRasterStorageDef(storageDef);

    var sel = MapView.Active.Map.GetSelection();

    //insert a raster value object into the raster field
    var insp = new ArcGIS.Desktop.Editing.Attributes.Inspector();
    insp.Load(sel.ToDictionary().Keys.First(), sel.ToDictionary().Values.First());
    insp["Photo"] = rv;

    var op = new EditOperation();
    op.Name = "Raster Inspector";
    op.Modify(insp);
    if (!op.IsEmpty)
    {
      var result = op.Execute(); //Execute and ExecuteAsync will return true if the operation was successful and false if not
    }
  }
});