How much length can veneers add to my upper teeth in accordance with my bite? (photos)

I noticed plaque and gingival inflammation in your photographs.  You need to get your gums healthy before proceeding with any cosmetic treatment.  Adding 5mm to the length of your front upper  teeth will give you a deep overbite, and adding this much length will make them very prone to fracturing.  I would recommend testing the amount of length that can be added with reversible, no prep cosmetic bonding.  This will not damage your natural teeth and can allow you to test drive the added length.  I would start by adding 1-2mm.  See how that looks and feels and live with it for about two weeks.  After that time, if you want additional length added, it can easily be done by adding to the bonding for another 2 week test drive(your dentist can advise you if and how much additional length can be added).  If the additional length creates too much overbite, your bite may need to be opened by adding to the chewing surfaces of your back teeth.  This can also be tested by adding bonded, no prep composite resin to your back teeth.  If you are comfortable and happy with the look and feel of the cosmetic bonding, you can opt to keep it as a permanent treatment for several years or longer with occasional touchups.  Or you may have it replaced with porcelain veneers and porcelain onlays on your back teeth (if required to open your bite) if that is your preference.

difficult to say anything without seeing yr case. its my advice to upload proper smiling pics so i can guide u better. there r many procedures for teeth lengthing . for eg. gingival surgery, braces/ aligners, veneers, digital smile designing etc. 

Do you really mean 5mm or is it supposed to be 0.5mm.  There is no way you could add 5mm. That would look very bizarre.  Your bite is very tight and you actually have cross-bites which would best be treated with Invisalign first to get your teeth into better position first. From your pictures, you have an excessive amount of bacterial plaque build up with gingivitis at a minimum.  You may actually have periodontal disease.  Have you been seen by a dentist recently for examination and cleaning.Once your teeth and gums are healthy, veneers could be made with some additional length to help make your teeth longer but nothing like your stated desired length.Please schedule an appointment for examination, cleaning and oral hygiene instruction before the plaque causes further decay and periodontal problems for you.Douglas Jopling, DDSDallas, Texas area