Based on some of the online identification keys/guides, I'd say it was either a bull (Zambezi) shark or a grey reef shark. They both can have very similar forms and coloration. The deciding difference (visual observation) between the two, AFAIK, is the small eyes and heavy body of the bull shark. The perspective of the image prevents making a clear judgement on that in this case, however. The dark edges of the second dorsal fin and the anal fin would tend to point the finger at the grey reef shark. That is, of course, unless it's shadow in the picture. That said, the dark edges (because the image is not crisp and clear) may point also at a dusky shark.
I may not be helping at this point. It is an interesting exercise, though. Thanks for the fun.
Checkout the id sites for yourself:
1.
www.elasmodiver.com
2. Queensland government shark id guide:
http://www2.dpi.qld.gov.au/fishweb/11825.html
3.
www.thaifishingguide.com
4. Shark and Ray encyclopedia on
www.coralrealm.com
Cheers,
Jay