Do I need a chin implant or sliding genioplasty? (photo)

I would suggest your first step be an evaluation by a board certified plastic surgeon experienced in facial aesthetics.  The best procedure will depend on your physical exam and possibly a cephalometric analysis.  A chin implant, sliding genioplasty, or jaw surgery may be indicated based on these studies.  One thing to remember, chin implant surgery is completely reversible while the others are not.  

A chin implant is a great idea for you.  Both procedures will work (chin implant and sliding genioplasty).  I do chin implants for persons such as yourself right in the office. It's safe, effective, and reversible.The sliding genioplasty I also do but that requires general anesthesia.

Given the severity of your chin/jaw deficiency, you would be better served by a sliding genioplasty. You have a horizontal chin deficiency that is cost to 20mms.  No standard chin implant exceeds 11ms which would still leave you deficient and would place a large implant load on your small chin. A sliding genioplasty will not only give you greater horizontal augmentation but would also vertically shorten your chin a bit. (an implant will likely make it look longer given the backward slope of the chin bone)  You may even need a combination of a sliding genioplasty with a chin implant overlay to maximize the horizontal augmentation and cover the lateral osteotomy sites.

 Hi, I have performed many facial shaping procedures using dermal fillers, facial implants (cheek, chin), liposuction and/or facelifts for over 30 years.  Following my beauty principles, men look chiseled and handsome with angularity in the cheeks, chin and mandibular angles.  From the photos, your cheeks are flat in the front, the chin is weak as are the mandibular angles.  The following procedures would create a more ruggedly handsome face.
Cheek augmentation with dermal filler or silastic cheek implants to add angularity to the cheeks and mid face. 
Chin augmentation, using a chin implant, to add projection to the chin creating harmony and balance to the lower face.  I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  When the chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy, the lower face looks short, de-emphasizes the lips and allows early formation of a "double chin".  Proper placement of a silastic chin implant adds forward projection to the chin thereby creating harmony and balance to the lower face.  Using the same incision, liposuction can be performed to reduce the fat and further shape the neck.  Excess skin, from below the chin, can also be removed through the same incision.  I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty (requires extensive tissue dissection, bone cuts and placement of metal screws and plates to secure the cut bone segments).  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  In my opinion, you are a good candidate for chin implant surgery.  
Augmentation of the mandibular angles using a dermal filler (jaw implants have too many unwanted side effects IMHO) to add volume, angularity and flare to the jaw line.
Hope this helps.