Perhaps I embarrassed you in my earlier post about unhelpful formatting. Sorry, I was actually trying to be (er) helpful.
But it is not only your text that must be delivered in a suitable format; so, too, must any illustrations. I briefly touched on this issue earlier with the cover design but essentially your image files must be usable – both readable and, for bit-mapped (rasterized) images, of a sufficient resolution (at least 300 dpi in its final dimensions).
If you are delivering any vector-based images, these of course can be scaled without problem (resolution is not the issue here). However, to avoid any readability problems for the typesetter, make sure that these images are in EPS format rather than the proprietary format for the software you use (most likely Adobe Illustrator and CorelDraw), especially since these programs can save files in EPS format.
Image readability/suitability is something that most likely your production editor will check as a matter of routine but you will not want to make a last-minute confession to her about the key illustration in your book being unusable (it is so grainy, it looks as if it were made with Lego blocks).
Such horror pictures cannot be fixed (well, not satisfactorily). Neither your editor nor the typesetter is a magician; they cannot fix everything. More to the point, they have better things to do with their time.
As such, if you have images in need of a bit of time, love and care (and you cannot provide this yourself), then I suggest you find yourself a technically savvy friend to optimize your images to the highest quality before you deliver them to your publisher.