This is not a new problem. I found this InDesignSecrets.com post from 2006 which points out the pasted graphics don't show up in the Links panel. Pasting basically takes control of the process from InDesign.
If you want an Embedded Graphic, you select a linked graphics and choose to Embed it from the Links panel menu. Then it shows up in the Links panel with a special icon.
However, a pasted graphic does show up in the Layers panel as a <pasted graphic>:
There is no preflight option, but here's a couple things you could look for in Preflight:
* Choose IMAGES and OBJECTS and look for low resolution images using Image Resolution. They are almost certainly low res images
* When I tested with images from Photoshop and Mac Preview, Preview made the graphics transparent. So you can also turn on Transparency Not Allowed. Photoshop doesn't make the transparent when you copy and paste.
Another thought: There is no way to search InDesign's Layers panel. But someone may have created a script to look for a <pasted graphic>. You might ask in the InDesign Scripting foru.
Thanks for your input, Steve. I'll look into both of those options. It really would be nice to have some way to see it in the links palette or something- especially when prepping final files with dozens or hundreds of images that get passed around. It's easy enough for someone to accidentally paste a graphic or image unconsciously. It would be great to have a way to easily see, catch and repair that kind of thing. It's pretty rare that I've come across this, but clearly it happens.
If you are using OSX you could also try this AppleScript. It's similar to Peter's script, but it links the pasted object out to a PDF which retains all of the original file info (color space and resolution) rather than converting it into a bitmap format: