CoreData : store images to DB or not?

First, always store your images in a usable format such as PNG or JPEG instead of NSData. This will save you a lot of headaches.

Second, the rule for storing binary data is:

• < 100kb store in the same table as the relevant data
• < 1mb store in a separate table attached via a relationship to avoid loading unnecessarily

• 1mb store on disk and reference it inside of Core Data

Update

The storage inside of Core Data should be binary and you can write accessor methods for it. Take a look at this answer: Core data images from desktop to iphone

Update

The example code I linked to describes how to create accessors in your NSManagedObject subclass that will convert the image back and forth between a UIImage and binary data.

You can simply store UIImage objects in CoreData directly, just use Transformable data type, and you are ready to go