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Old 04-09-2011, 01:08 AM   #1
Alissa
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Question Where else can a MOBI file have its cover image?

Hi, MOBI file experts,

I'm having some problems to develop my MobiHandler program. One of them is a cover image.

I noticed that my MobiHandler can't show cover images for some particular .azw files bought from amazon.com, while K4PC can on its HOME window. One example of those files is My Blood Approves by Amanda Hocking.

I hex-dumped it and manually checked the structure based on the info. on mobileread wiki, but I found nothing unusual; it looks like an ordinary MOBI file with no image files inside.

Where else can a MOBI file have its cover image but an image record?

One possibility might be the cover image is encrypted, since those books are DRM protected, and their book texts are unreadable on hex dump.

Any idea?
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Old 04-09-2011, 10:52 AM   #2
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I know nothing about Kindle's DRM, and very little about the structore of mobi files, but I do know that if you want to download a DRM-free kindle book from Amazon for comparison, none of the books published by "Twilight Times Books" should have any DRM at Kindle.

(Edited to add: There may be other non-DRM Kindle publishers too, it just happens that this is one I'm sure doesn't add DRM.)

Some of them are available for free from time to time, and several are priced at $0.99. so you could experiment without too much cost.

Last edited by st_albert; 04-09-2011 at 10:57 AM.
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Old 04-09-2011, 03:26 PM   #3
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I don't know how/where K4PC get its covers when K4PC shows a different image than the one that's part of the mobi. K4PC may be downloading an image based on the ASIN number for all I know.

Mobi's may have a thumbnail cover image in addition to the cover image:
1) The four bytes contained in EXTH Record Type 201 are added to the first image field (offset 108 of the mobi header) to find the cover image's PDB record.
2) The four bytes contained in EXTH Record Type 202 are added to the first image field (offset 108 of the mobi header) to find the thumbnail cover image's PDB record.

* But you probably know all that already since you referenced the Mobi Format Wiki here on MR.

Last edited by DiapDealer; 04-09-2011 at 03:29 PM.
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Old 04-09-2011, 08:56 PM   #4
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Under Windows XP, K4PC stores cover images in
Code:
C:\Documents and Settings\<UserName>\Local Settings\Application Data\Amazon\Kindle For PC\Cache\covers
I assume these are downloaded from Amazon's servers if the ebook has no included image.

EDIT: I now think any new covers are downloaded from Amazon servers whenever you open K4PC. I see covers there for ebooks that I have never downloaded to my PC, and the covers downloaded today are for my recent ebook purchases. This probably means that K4PC never looks inside the .azw file for the cover. With this approach it can always show covers for "Archived items"

Last edited by wallcraft; 04-09-2011 at 09:11 PM.
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Old 04-11-2011, 08:54 AM   #5
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Quote:
Originally Posted by wallcraft View Post
Under Windows XP, K4PC stores cover images in
Code:
C:\Documents and Settings\<UserName>\Local Settings\Application Data\Amazon\Kindle For PC\Cache\covers
I assume these are downloaded from Amazon's servers if the ebook has no included image.

EDIT: I now think any new covers are downloaded from Amazon servers whenever you open K4PC. I see covers there for ebooks that I have never downloaded to my PC, and the covers downloaded today are for my recent ebook purchases. This probably means that K4PC never looks inside the .azw file for the cover. With this approach it can always show covers for "Archived items"
Wow. I too find many cover images in the directory. Some are cover images from ebooks with embedded cover images, as you wrote. However, I don't see some cover images there whose covers are shown on my K4PC HOME window... I don't know when a cover image is stored there and when isn't.

Also, I noticed that the file names of .jpg files there are all 32 hexadecimal digits. I guess they are some hash values (MD5?) of something. If there names followed filenames of .azw or ASIN, I could look into the folder for missing cover images...

Anyway, thank you for interesting info.
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Old 04-12-2011, 03:02 PM   #6
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Quote:
Originally Posted by DiapDealer View Post
K4PC may be downloading an image based on the ASIN number for all I know.
I'm pretty sure that I have seen exactly this, back when I was manually adding ASIN's to allow sync of reading location.
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Old 07-13-2013, 02:50 PM   #7
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Quote:
Originally Posted by st_albert View Post
I know nothing about Kindle's DRM, and very little about the structore of mobi files, but I do know that if you want to download a DRM-free kindle book from Amazon for comparison, none of the books published by "Twilight Times Books" should have any DRM at Kindle.

(Edited to add: There may be other non-DRM Kindle publishers too, it just happens that this is one I'm sure doesn't add DRM.)

Some of them are available for free from time to time, and several are priced at $0.99. so you could experiment without too much cost.
Kindle books by Andrew Greeley don't have DRM, at the publisher's request, according to their pages on Amazon.

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