Why can't I view photos shared on iCloud?

My mom sent me a some photos through photosharing on iCloud and I received the invitation in my email and clicked subscribe. I cannot access the photos. I have 10.10.5 and my mom just got El Capitan. Since installing Yosemite, I no longer have IPhoto but it was replaced with photos. This is what I get even though I already hit subscribe in the email message- HELP:

iCloud Photo Sharing is not available for this device

To subscribe to XXXXX dogs” shared album on your iPhone, iPad, iPod touch, or Mac, open your invitation in the Mail app, and click the Subscribe button in the message.

To subscribe you need to be signed in to iCloud on:

• an iPhone, iPad, or iPod touch with iOS 6 or later, or
• a Mac with OS X 10.8.2 or later and iPhoto 9.4 or Aperture 3.4 or later