I recently posted a question regarding recovering a DDD architecture that became an anemic domain model into a multitier architecture and this question is a follow-on of sorts.

My question is when do domain concepts become application constructs.

My application is a local client C# 4/WPF with the following architecture:

Presentation Layer

• Views
• ViewModels

Business Layer

• ???

Domain Layer

• Classes that take the POCOs with primitive types and create domain concepts (e.g. image, layer, etc)
• Sanity checks values (e.g. image width > 0)
• Interfaces for DTOs
• Interface for a repository that abstracts the filesystem

Data Access Layer

• Classes that parse the proprietary binary files into POCOs with primitive types by explicit knowledge of the file format
• Implementation of domain DTOs
• Implementation of domain repository class

Local Filesystem

• Proprietary binary files

When does the MyImageType domain class with Int32 width, height, and Int32[] pixels become a System.Windows.Media.ImageDrawing? If I put it in the domain layer, it seems like implemenation details are being leaked (what if I didn't want to use WPF?). If I put it in the presentation layer, it seems like it's doing too much. If I create a business layer, it seems like it would be doing too little since there are few "rules" given the CRUD nature of the application.

I think all of my reading has lead to analysis paralysis, so I thought fresh eyes might lend some perspective.