n tier architecture - External API Calls - Data Access Layer or Service Layer?

I have an N-tiered application:DatabaseDomain LayerData Access LayerService LayerPresentation Layers (iOS, Android, MVC 3)I am trying to employ the Google Api for Picasa for users to upload photos. Where is a good place to put the logic for uploading functionality, picasa authentication in the Data Access Layer or in IImageService within my Service Layer?I think it should be within the Service Layer but I am not totally sure. I also have a Domain Class for Images public class Image { public int ImageId {get; set;} public string Name {get;...Read more