BASIC MOTION TRAILS
This is called Motion Blur in Imagemagick.
This is not a do all tute ~ Just the basics.
I took this and a 350x350 black graphic to IM and composited it using Northwest ~ Parameters ~ +10+10 which looks like this.
Then taking it to Effects ~ Parameters ~ 200x150+225
Clicked Motion Blur and got this.
Then I composited the clock ( original image ) over using Northwest ~ Parameters ~ +10+10 I got this.
Note: If you plan on compositing the motion trail graphic over another graphic you will need the background to be transparent. You will have to output as a png or the background will not stay transparent.
Note: The first two numbers in the parameters determine the length of the trail. The bigger the numbers the longer the trail will be. If you use too big of numbers you will get a popup saying IM is too busy.
Note: The last number in the parameters is the direction of the trail.
Here are a few samples for the some of the directions.
+ Parameters for trail direction
100x100+0 | 100x100+90
100x100+180 | 100x100+225
100x100+45
- Parameters for trail directions
100x100-90 | 100x100-45
Note: You can use any number from 0 to 359 plus or minus
Here is one option I thought of. Will have more when I think of them.
OPTION I
You say you would like more colors in that trail? You can.
I used the same steps as above but before I used Motion Blur I annoted a period of large pointsize like this did the Motion Blur composited original graphic over and got this.
I also did this and got this.
I thought about this but didn't try it untill I saw Cali Kat post one with it done. I'm sure you have seen motion trails that were not straight. This is the way to put a curve in it.
OPTION II
I composited a transparent graphic ( png ) over a xc made in IM. I then did a Motion Blur. Then I went to FX and did a swirl at -40 and got this.
You will notice the trail looks kinda funny. That's because it is a png. It will change when you composite it over a graphic with some color in it like this
Here are a few things I have tried. I made this with a dingbat and turned it into this using unique colors and composite.
Have you seen the pearl motion trail around? You can do that. Have a look at this.
You can use this on fonts.
You can also use a colored background instead of a transparent one.
I'm sure other ways will be found to use this.
This ought to get you started on something you could only do in the past with a pc....{•;
Here are some people that have figured out some unique ways to use motion blur.
Pj's Textured Frames
MsV's Edge Detect with Motion Blur | 
