I ended up just using actors. It worked better than trying to figure out the image API. I'd say that the level of complexity of the image API is not simple like the rest of stencyl and it kind of stinks that this program is marketed as simple but it really just isn't very handy for people who aren't wizards at it.
The code JeffreyDriver uploaded is
literally the
EXACT code to get the trail working; in fact I copied it word for word and got it working in 5 minutes(ty Jeffrey, lovely trail effect). My guess is, you created incorrect attributes and plugged them into the incorrect field. Using actors to achieve this can be detrimental to optimization and in larger scale projects is definitely a no-no but if this is just a "whatever" project then I guess..
Image API is definitely not something I would expect a beginner to grasp especially if that's the first thing you want to achieve in your project; however, it definitely doesn't take a "wizard" to utilize most of what Stencyl has to offer. Imo, Stencyl offers a good balance between casual game developers and those who wish to utilize more advanced features but don't be hard on yourself for this minor road block. I, personally have spent weeks/months trying to hash out small bugs or learn new features and we all go at our own pace so don't feel like you need to be a "wizard" just yet. cheers!