Camera? Neither of my suggestions involved the use of a camera.
Apparently, there is a degree of miscommunication present in our discussions.
In your original posting:
The above quote seems to suggest you are attempting to monitor the speed of a vehicle utilizing a sensor mounted on the said vehicle. Is this correct?
What microcontroller are you using in your design?
By implementing a tachometer utilizing a simple IR TX/RX pair coupled with a IR reflective marker on a portion of the vehicle's drive train, e.g., wheel, drive shaft, etc, the associated RPM of wheel or drive shaft can be easily obtained and used in the calculation of the vehicles speed.
Tachometer/RPM II.
DIY PIC Microcontroller Based Digital Tachometer Project
How to make a contact-less digital tachometer using IR-light reflection technique
The following thread provides and in depth discussion of implementing a RPM tachometer using IR sensors:
[SOLVED] some questions motor speed monitoring
The other method that was previously mentioned utilized a Global Positioning System (GPS) module, which would provide not only speed (velocity), but heading and current coordinates as well.
GPS uses orbital satellites and a GPS receiver module to obtain a constant update of various information, including velocity.
The modules range in price from $30 USD to several hundred per unit depending on the desired features.
**broken link removed**
Hope the info helps in your endeavors,
BigDog