My apologies for getting behind in the discussions. I was on deadline with a magazine assignment (which I filed today !! Yay !! )
My understanding -- and someone correct me if I'm wrong -- is that we're doing an 8.5x11" book in vertical format (spine along the long edge). I didn't see any other options for orientation on the Lulu site, though I may have missed it.
Now, of that 8.5" width, subtract 0.5" for gutter space, where the book is bound. That leaves 8". If your longest length horizonal image is 7" that only leaves 0.5" white space around it. 6.5" would leave 0.75" white space, which would probably make the image look better.
Portrait orientation prints have more room on the page and could easily go to 9" on the long edge.
Or we keep all photos at 6.5" or 7" on the long edge for uniformity.
I don't think we should set a set size on the short edge because some images may be cropped and others printed full frame.
My math reads like this (someone check the figures):
7" x 300dpi = 2100 pixels on the long edge
6.5" x 300dpi = 1950 pixels on the long edge
9" x 300dpi = 2700 pixels on the long edge
The short edges will fall however you crop your image.
So, for example, in Photoshop you would do Image Size 300dpi and set the long edge to 2100 pixels if we decide to do 7"
This weekend I will try to mock up four image pages to scale that you can download and print out on your printer to see what you think works best.
Also, don't think in terms of image size in KB. This is usually a factor of resolution + which colours are in the image. B&W's are usually smaller than col images, but not always. Dark images are usually smaller than bright ones. The key thing is getting the 300dpi and the correct number of pixels on the long edge and letting everything else fall where it does.
Gene