Think of the iCloud library as one library that exist in the cloud. Setting aside the moment between when you turn it on and when all of the photos are uploaded for just a moment, each of your devices will have some mail of every image in the library as well as a larger version of the file.
On a device per device basis you can request the original sized file or let the system shrink, compress, optimize when storage runs low.
This design works well for people that just want to have one library and not several versions of the library. The point of iCloud photo library is if you have a 50 GB library total, you'll still end up with the same number of photos on each device even if the entire library size is 10 GB on an iPhone 30 GB on an iPad and 20 GB on your Mac.
The compression only kicks in once your space gets low on a specific device. I believe there are several settings of compression so that as you begin to fill up your storage with things other than the photo library, the images can continue to shrink up to the point where you have nothing left but thumbnails, presumably.
In short, disabling iCloud should keep your photos on your device. To turn it off, navigate to "System Preferences" > "iCloud" and click the "options" button next to "Photos". Deselect "iCloud Photo Library" and "My Photo Stream" (as below).
Note: On iOS turn this off under the iCloud setting, not the Photos & Camera settings.
To answer the question
...is there any way to delete my iCloud without deleting all my photos?
Turn iCloud Photo Library off. I have tested this on my Mac and all my photos are still there. You can not delete iCloud because it is a service, not a place or thing. Hence you just stop using it.
If the Mail Man stopped delivering letters, you still get to keep the ones you already have.
Can I do this, and if so, how?
By definition synchronisation (sync) means to make the same. So iCloud will do whatever it can to make sure all your devices have the same content for everything. This is obviously not what you want.
However, there are three main parts to iCloud photos, not just the syncing bit.
- iCloud Photo Library (the syncing one I assume you have enabled – a.k.a sync everything)
- My Photo Stream (upload only new photos you have taken to all devices)
- iCloud Photo Sharing (upload selected albums).
Think of these as three different services. You want to enable iCloud Photo Sharing so that you may select only the albums you want to keep in sync. As far as I'm aware, iCloud Photo Sharing does not store pictures in iCloud like the photo library does. It says below, this is for sharing with other people, but you can just add yourself when sharing the album.
To share albums
On Mac, select an Album you which to share, then click the share button. Click "iCloud Photo Sharing", then the big plus to add the album. Now just add yourself as a contact in the "invite people" section.
On iOS, there is a little cloud symbol at the bottom of the screen in the "Photos" app labeled "Shared". If it is empty, it will guide you though it.
Best Answer
This is possible by opening the Settings.app on your iPhone, scrolling down, and selecting "iCloud". Scroll down, then tap Storage & Backup -> Manage Storage -> [Your iPhone Name] (This iPhone). You will then see a list of all the apps that are storing data in iCloud. Chances are the top one will be "Camera" and you can switch that off. Doing that will delete photos from iCloud, and if you were to ever restore your phone, photos would not be restored. However, it will not delete the photos that are on your device already.
Also, it is important to note that iCloud Shared photos, as well as your Photostream do not count toward your iCloud backup storage limit. There is an arbitrary limit of 1,000 photos on your Photostream. You can safely leave those on without affecting your storage use amount.