Are these stains or tooth decay? (Photo)

Just looking at the picture or photo, small decays can not be diagnosed. See a dentist for clinical exam, xrays and consult. 

It is difficult to tell from the photos provided but it appears you have some decay at your gumline and deep yellow stains. If it is decay, it needs to be diagnosed by a dentist and treated before any whitening can occur.

It appears that you have some staining on your teeth. This can happen during orthodontic treatment because it is more difficult to clean effectively around the brackets and under the wires.
Your teeth are also rather discoloured generally. I would suggest seeing your dental surgeon and initially ask to be referred to a hygienist to remove surface stain and receive any oral hygiene instruction. 
It would also be worthwhile asking your dentist about tooth whitening. This can be either home whitening or in-surgery,. At my practice we use Zoom in-surgery whitening to achieve an immediate improvement in shade and follow this up with whitening trays and gel to be used intermittently afterwards in order to maintain the shade.
Best wishes
Dr Ian Hallam MBE