I have a CMYK file, outlined product, that looks perfect in Photoshop. When I place the image into Illustrator, it shows up with a thin white line around parts of the product (fyi - it shows up on a print as well). I have tried to place an RGB file and it does not have the white line around the product. I assume it has something to do with it being CMYK, but I'm at a loss on how to fix this. I'm desperate for any help.
This happens when you place a rasterized image on a gradient background. There is a known bug in Illustrator as well as Acrobat due to this issue. In Acrobat, under preferences > Page Display, uncheck the options "Use 2D graphics acceleration" and "Smooth line art", and then click Ok. You will see that the thin white lines disappear.
I have this problem in illustrator when placing an image onto a black background. Like shnath said, it is a known glitch in illustrator. I usually change the blending mode to Multiply and the line goes away. This might not work in your case though, but try it out.
I have found the error to be cause by importing images (PNG) with transparency. So what I did is OBJECT > FLATTEN TRANSPARENCY (check the options are the way you want them, anti-alias OFF might help). Then to create the transparency I created shapes in AI itself and created a clipping mask. This solved if for me.