As you can see in the screenshot below, a new Upload button has been added to the top right of the toolbar. Click it to easily upload JPEGs from your computer to iCloud Photos.
Once you've added a photo via the web browser, it will sync across your iOS devices.
For more details on enhancements to Photos in iOS 8 click here.
Notably, Apple has announced a new Photos for OS X application to compliment iOS 8's new photo features. Photos will be replacing iPhoto and Aperture, which has upset many power users. However, Apple says the new application will include many power-features such as image search, editing, effects and third-party extensions.
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