What alternatives are there for teeth whitening? (Photo)

Thanks for your question. There are two types of staining that darken teeth, extrinsic and intrinsic. Extrinsic stain is on the surface of your teeth and can be removed. For this I always recommend a professional cleaning at a dental office. The cost might be more reasonable than you think, and it really is investing in your health. Not only can they remove stain, but a professional cleaning can help prevent problems that can lead to tooth loss. Whitening toothpastes are abrasive and can help remove the stain, but they can also cause damage in some cases. 
Intrinsic stain is stain that has been absorbed into your teeth. This can be removed by bleaching. Over the counter products such as Crest White Strips usually work for bleaching teeth, they are just slower than in-office bleaching.
Finally, staining can also be caused by other problems like decay or hardened plaque on your teeth. An evaluation by a dentist is crucial to make sure you don't have any bigger underlying problems that are causing your teeth to darken. 
I hope this helps!