What size should my photos be for my Blurb book?
If you're looking for a simple answer, like 8x10 inches or 3872x2592 pixels you may be disappointed. There's no one-size-fits-all answer because it depends on the resolution of the individual photo.
Our free bookmaking software, BookWright, requires a minimum resolution of 250 PPI (pixels per inch). As you increase or decrease the dimensions of your image that reduces or increase the PPI, respectively. Sizing your image so that it's less than 250 PPI will trigger a low-resolution warning. (Our other design tools have similar low-resolution warnings).
So if you place your image onto the page/into a container at 8x10 inches and see the "!" resolution warning then 8x10 (or whatever it might be) isn't the right size--for that image. You'll need to make the image smaller on the page (or zoom out) until the resolution warning goes away.
However, a completely different image, captured with larger dimensions and a higher resolution setting, may work just fine at 8x10 (or 11x14, or whatever the container size might be). It depends entirely on the characteristics of that photo, which is the result of the camera settings at the time you took the photo.
That's why there's no simple answer to the question What size should my images be? The answer is ultimately 250 PPI at the size you plan to print them.
Can I fix my low-resolution images?
Yes--by making the image smaller on the page or using a different image.
And while you can't make a small, low-resolution image better you can plan for the future: if your camera gives you the choice, capture your photos at the largest size (the image size setting) and the highest image quality setting--usually Fine. A large image taken with the Fine quality setting will be much more versatile than a smaller image taken at a lower quality setting.
Alternatively, if your camera gives you option for RAW files you can choose that instead. Shoot in RAW, then convert the RAW files to large, high-quality JPG or PNG files later. That versatility is worth the small amount of extra disk space the larger RAW files (or large, high-quality JPG files) will require.