DPI only really matters with print, but it does influence file size. I only have one image embedded in one of my books, so I'm not really the best to answer this, but I do know that your overall epub file size can be no more than 20MB. So if you file size is the tiniest bit over . . . well . . .
I would try to lower the DPI as low as it will go and try that first before I tried to resize any images.
DPI is only for printing. Insert your image into the Word document after a page or section break where you want it in the text. Have the page size 8 1/2" by 11" I used 1" margins. The image will fit to the page. Odds are, your images are too big. The images have to be inside the document and it is all one file. I used Word 2003 and saved as ,doc. If you use Word 2007 or 2010, save as Word 97-2003. If you need to, ask more questions. Melissa may come along and add more in case I've forgotten something.
I will check the document for sizes of the pictures. By which you mean size in inches I gather?
I forgot to say inches. 8 1/2 by 11.
Ereaders have different size pages..
I used JPEG to save the images. Some other image formats are too big. I know that from uploading images to my blog. I have had to change the image format to JPEG.
I used MS Paint, drawings. Word says to save as PNG. Nope. It bled colors. I used JPEG and it was fine.
The outdated PubIt! ePub Formatting Guide (2010) by B&N indicates that the pixel dimensions of images should be sized to fit the Nook e-reader display. In 2010 all Nooks had an available display size of 600 x 730 pixels (they actually had a native resolution of 600 x 800 pixels).
This is why DPI (dots per inch) and PPI (pixels per inch) are unimportant. DPI matters to a printer who needs enough image pixels to create a good halftone pattern on the printer. I'm pretty sure all e-readers ignore the DPI setting inside an image file. They only look at the pixel dimensions.
There have been a number of Nooks since 2010 that have bigger display specs. Here are the current models:
Nook Simple Touch: 6-inch, 600 x 800 pixels, 167 ppi, 4-bit grayscale
Nook HD: 7-inch, 900 x 1440 pixels, 243 ppi, 24-bit color
Nook HD+: 9-inch, 1280 x 1920 pixels, 256 ppi, 24-bit color
You'll have to decide which of these resolutions to target. If you choose 1280 x 1920, your images should be automatically scaled down by the Nook e-reader software on the e-readers with smaller displays. But you may not like how the scaling is accomplished (Will some sort of pixel averaging be used or will pixels simply be thrown out?). I advise doing some tests if your images need to display sharp-as-possible detail (for example: your image is a map or contains small fonts).
My approach is to use the smallest image size when possible. I would use the 600 x 800 (or 600 x 730) if I didn't need the maximum pixels on the HD Nooks.
What are the pixel dimensions of your images?
What file formats do your images use?
What are their file sizes?
Kind regards, David
Hey, Janico, thanks for posting this image uploading issue here. But it would be great if you marked the right answer. It spent me more than 10 minutes looking for the answer (I am not native English speaker, so...)