Currently Being ModeratedDec 9, 2012 5:43 PM (in response to Wrangle)
The last email 5.22.12 on this topic said this about that:
We are changing the minimum size for cover images. Cover images should now be 1400 pixels wide, in the RGB color space, and delivered as JPEG files. The new minimum size for cover images will be a requirement starting this August. Books already available on the iBookstore do not need to be redelivered.
Currently Being ModeratedDec 11, 2012 10:23 PM (in response to Wrangle)
I uploaded screenshots straight from an iPad 3 (PNGs from a Retina display, 2048 x 1536, horizontal and vertical), and had no problem with that.
Currently Being ModeratedDec 12, 2012 4:35 AM (in response to Wrangle)
iBookstore Asset Guide 5.0
● Full-sized iPad 1/2 images (1024 x 768 or 768 x 1024) in PNG (.png) or JPEG (.jpg) format.
● Full-sized new iPad images (2048 x 1536 or 1536 x 2048) in PNG (.png) or JPEG (.jpg) format.
● For a cleaner look, you can optionally remove the status bar (making the images 1004 x 768 or 748 x 1024
for iPad 1/2, or 2028 x 1536 or 1536 x 2028 for the new iPad).