if I understood it well Faracus, Google map api works better with square for images.. you should maybe try making it square and center it correctly on your new jpg... And then you will also have to hope that it won't be too hard to convert GTA points to Google map points..
Good luck !
Also, apparently some think that my previous post was an advertisment... if you also feel this please just tell me and I remove it... Otherwise just tell if we can help :D