As clarified in the comments, you are seeing the result of dragging thumbnails (instead of the actual picture) directly from Photos on Mac into iCloud Photos. As your version of Photos/macOS is too old to support iCloud syncing, there are alternatives:

• If your version of Photos supports this: right-click on a photo in Photos, select "Reveal in Finder", wait for Finder to open the window and then drag&drop the picture into iCloud Photos.
• Otherwise, right-click on the Photos library in ~/Pictures, select "Show Package Contents" and look for the photo in the appropriate sub-folder.

As clarified in the comments, you are seeing the result of dragging thumbnails (instead of the actual picture) directly from Photos on Mac into iCloud Photos. As your version of Photos/macOS is apparently too old to support iCloud Photo library syncing, there are alternatives:

• If your version of Photos supports this: right-click on a photo in Photos, select "Reveal in Finder", wait for Finder to open the window and then drag&drop the picture into iCloud Photos.
• Otherwise, right-click on the Photos library in ~/Pictures, select "Show Package Contents" and look for the photo in the appropriate sub-folder.

As clarified in the comments, you are seeing the result of dragging thumbnails (instead of the actual picture) directly from Photos on Mac into iCloud Photos. As your version of Photos/macOS is too old to support iCloud syncing, there are alternatives:

• Instead of dragging the thumbnail, double-click the photo to open it in Photos and then drag&drop the full picture into iCloud Photos.
• If your version of Photos supports this: right-click on a photo in Photos, select "Reveal in Finder", wait for Finder to open the window and then drag&drop the picture into iCloud Photos.
• Otherwise, right-click on the Photos library in ~/Pictures, select "Show Package Contents" and look for the photo in the appropriate sub-folder.

As clarified in the comments, you are seeing the result of dragging thumbnails (instead of the actual picture) directly from Photos on Mac into iCloud Photos. As your version of Photos/macOS is too old to support iCloud syncing, there are alternatives:

• If your version of Photos supports this: right-click on a photo in Photos, select "Reveal in Finder", wait for Finder to open the window and then drag&drop the picture into iCloud Photos.
• Otherwise, right-click on the Photos library in ~/Pictures, select "Show Package Contents" and look for the photo in the appropriate sub-folder.