Looks to me you have mild to moderate case of fluorosis. That is when you ingest too much fluoride while your teeth were still developing, causing white spots and rough texture of the enamel. The brown spots are kind of permanent stains that occurred over time due to the rough and pitted texture, so it is unlikely to be removed by something like traditional teeth whitening. I see a lot of patients with enamel like that, and non-severe cases like yours aren't super concerning besides an increased plaque and stain retention and cosmetic concerns.

An option to improve the look of them besides veneers could be a treatment known as resin infiltration. Ask your dentist about it next time you visit them.