The new Google Photos service offers unlimited storage for "High Quality" images which are 16 Megapixels or less, but if you are using pictures which are over 16 MP, you might choose "Original" storage, but this consumes space on your Google Drive (you get 15 GB free storage on Google Drive by default).
The on-line Help says:
If the camera takes photos with 16 megapixel (MP) resolution or lower, most stored photos will essentially look the same using either storage option.
If the camera takes photos with a resolution higher than 16 MP, then photos will be downsized to 16 MP.
https://support.google.com/photos/an..._topic=6131427