How can we ensure that contact photos appear as either full-screen or as thumbnails on the iPhone? I've noticed that contact photos on the iPhone seem to appear in one of two modes:


Thumbnail: A small square image shown next to the contact's name or number
Full-Screen: The image takes up the entire display, overlaid by the caller ID and Swipe-to-answer controls


How the phone determines which mode to use isn't terribly clear. This question, for example, dealing with contact syncing, seems to have people experiencing different results depending on whether they set the photo on the phone, synced from Gmail, synced from iCloud, etc.

Does anyone know the canonical rules for when a contact image appears in full-screen or as a thumbnail? Is it related to image size / shape, or only to the source of the image?
In my testing1, pictures set on the iPhone itself consistently appear as full screen, and pictures set in Address Book on OS X and synced via iCloud appear as thumbnails. Any photos set elsewhere, but subsequently edited on the iPhone will also appear full screen.

I haven't tested other syncing methods, but from what I've read elsewhere, including the question you linked, I think the syncing method doesn't matter — just whether the photo was set on the device, or on a Mac.

It's hard to say why exactly without any inside information, but I suspect it's one of two reasons:


Different teams worked on the syncing and iOS Contacts app (or at least the user facing portions thereof). Some flag gets set somewhere in the data structure when you set a photo in the Contacts app that doesn't get set when a photo is synced over. Just something that got overlooked.
Intentionally left out. Since you don't get the opportunity to preview the cropping and alignment on the device screen when setting it, it was decided to make pictures assigned off-device just appear as thumbnails, to avoid any bad cropping or weird aspect ratios.


In any event, if you want consistency, you should set all your contact pictures on the same device — Mac if you want thumbnails, iPhone if you want full-size.



1 I tested on iOS 6.0.1 on an iPhone 4S, and 10.7.5 on my Mac.