How do I get my Apple TV to display Photo library?

You can use home sharing, just switch the source to the photos app within iTunes (file -.home sharing - choose photos to share)

As far as streaming directly, that is not yet supported

Make sure iTunes is up to date

I found the same issue trying to update pictures for the AppleTV3.

From what I can determine the issue is in iTunes itself not being able to select the new Photos app file format.

You will note that if you look inside your "Pictures" folder there is a new file called "Photo Library.migratedphotolibrary" (which is really a database of existing iPhoto pictures), plus a new file "Photos Library.photoslibrary".

Well, for whatever reason, it appears Apple missed or forgot that iTunes needs to be able to read the new file. Of course you can see your existing iPhoto pictures inside of Photos, but when it comes to being able to select them to share in iTunes, it just is not selectable - so much for the "IT JUST WORKS" factor - yet another defect from my perspective.

Besides this being some form of defect, it really is not intuitive that you have go into iTunes to select photos for the AppleTV. Or, rather it is not obvious as the Apple TV does not show up like the other iOS devices. User Experience (UX) is a hide and seek feature.

Working just fine on my system. Apple TV has no syncing ability so there is no reason it should show up like other IOS devices. Home sharing is done through Itunes.

Yes, I was able to select Photos as a source and they are displaying via the Computers icon. There is no support for direct streaming yet.

I'm not sure what vazandrew is saying.

I would like someone else to confirm that with Yosemite 10.10.3, iTunes 12.1.2.27, Photos 1.0 (209.52.0) and AppleTV3 7.2, and they are able select pictures by File -> Home Sharing -> Choose Photos to Share with Apple TV, and actually be able to choose photos to share from within the iTunes app.

There was nothing unclear about my response. Again, it is working just fine on my system

Okay, now that does make it clearer. Because I cannot get the "Photos" to appear from the selection:

Only the folder structure, not the App like is shown in your screen capture.

Question, which of you are using iCloud Photo Sharing out of Photos?

My preference is to share from pictures on the local Mac in lieu of sharing from iCloud.

What does the drop down menu look like? I assume you've rebooted and the Photos app has migrated all content from iPhoto.

The photo stream would be available directly on Apple TV (the new iCloud Photo Library is not yet supported), when going through iTunes it is to use home sharing (sharing photos from the local Mac)