My first choice would be to do that in post.

There is a feature in After Effects, also in Flame and Fusion, that is called "Scatter" that does precisely this.

However if you feel you MUST do this in Maya, check the help on emitting particles based on the RGB values of a texture image.
These particles will also inherit the rgb color value of the pixel it is born from.

Keep in mind that this CAN take a long while to calculate depending on your machine.

There are also a few melscripts that do what you need available on Highend's mel-scripts area for Dynamics.

Good luck!