GR8 intra-oral photography!!!
These look like stains of fluorosis.
After a thorough sub-gingival scaling following are your options:
please consult a COSMETIC DENTAL SURGEON in your area for further guidance/treatment.
These are generally hour-long chair-side procedures & they will definitely improve your looks dramatically.
Stopping/cutting down on your smoking
will be the best thing for you.
Thanks & All the best