I'm trying to create an emitter in particular that will allow me to use a library of images as the particle texture.
Here's what I'm doing:
I have 30 or so images that need to be emitted all from the same point. Each particle must have a custom teardrop shape. The shape of the particles will be the same throughout, only the texture/image/fill of that shape will need to be different.
Make a comp which is 30 frames long and not too big...maybe 400 x 400. Import all of your images into that comp as layers. You should have all 30 in the timeline. On the first frame, with all 30 layers selected, hit "alt-]" This will trim all the layers to one frame. With the layers still selected, right click and then choose keyframe assistant...sequence layers. This will stagger the layers so that each image is on a different frame. Next, create a new solid and use the pen tool to draw out your teardrop shape. Make sure this layer is on top of the layer stack and change the transfer mode to stencil alpha. Now each layer on the timeline should have the same shape. Move any layers around to center them in your shape.
Next, create your main comp and import your particle source comp you created above. Make a new solid and put particular on it. Change your particle type to sprite or textured poly if in version 2.0 or custom is in 1.5 and prior. Choose the particle source comp as your texture source and then change the timing option to be random still frame.
Now all of your particles should be one of the images you had in the precomp in a teardrop shape.