can you transfer data from a external hard drive to iCloud, without putting the data onto your mac first?

You can do it through a web browser on your Mac.

1. Connect the external drive
2. Go to www.iCloud.com and sign in with your Apple ID & password
3. Click iCloud Drive
4. Then the upload button (cloud with arrow) at the top of the screen
5. Navigate to the external drive and select the files to upload

If you have iCloud Drive enabled on your Mac (System Preferences > iCloud) then the files will be on your Mac.

Sounds to me like you want to enable iCloud Photo Library. This will allow you to store all your photos in iCloud and access them from your Mac running OS X 10.10 or later, an iPhone, iPad or iPod Touch (5th generation) running iOS 8 or later, or on iCloud.com via a web browser.