Epub cover malfunction.

icearch · 03-22-2026, 05:31 AM

How does cover work in epub?

I mean, how do software determine what to display as thumb nail?

I am being lazy and use a old file to save as a new file to make a new book, since they share same structure. Then I just sawp the cover image in Images folder to a new one, leaving cover.xhtml as it be.

Previewing in sigil looks fine, and getting into the book shows cover correctly as well. But thumb nail in reading app becomes random image in the file, or just do not display at all.

How does this happen? Where do I left unchageed?

Turtle91 · 03-22-2026, 07:53 AM

Thumbnails are generally handled by the reading device/app so you’d need to follow whatever requirements they impose.

Assuming the original epub worked properly and all you did was swap the image, then I would make sure the image references were exactly the same. Something as simple as a capital letter in the file name can cause an error as some software is more strict than others.

"Cover.jpg" does not equal "cover.jpg"

Also, some software uses the first image in the file list as the thumb. Capital letters can cause the image order to be rearranged.

Logo_publisher.jpg could appear before cover.jpg

For simplicity and consistency, I make sure to use all lower case letters in image file names and use underscores instead of spaces. I also make sure the cover image comes first alphabetically. In Sigil that is shown by the cover image appearing at the top of the list in the book browser pane.

icearch · 03-22-2026, 08:23 AM

I see the problem. When I deleted the old cover img,
<meta name="cover" content="cover-f.jpg" />
was removed in content.opf.

After adding that back it becomes normal.

The thumbnail software choose is the first pic in alphabet order in Images floder.

I created a new clean file and using add cover function in Sigil to observe this.

I might consider rename my cover pic to "001-cover.jpg" or something to provide fallback.

jugaor · Yesterday, 03:05 AM

Hi, icearch.
If you're already using Sigil, you can directly replace the image (without deleting it first) with a new one of the same name.
In the following dialog, clicking "Yes" will keep the "Cover Image" property in the new image.

Click image for larger version

Name: replace.jpg
Views: 8
Size: 14.2 KB
ID: 221996

[P.S. If you're in a real hurry or using a device without Sigil, opening the epub file with a zip-compressor and replacing the image will achieve the same effect… although it won't pass validation (due to the relocated 'mimetype'), most apps will open it without problems. For a quick personal test, it works.

]

icearch · Yesterday, 08:42 AM

I see, thanks.

JSWolf · Yesterday, 08:53 AM

For ePub2 or ePub2 fallback, this is the code in the OPF you use to specify the cover. The top line goes in the metadata.

Code:

<meta name="cover" content="coverimg"/>

For ePub3, you use the following. For ePub2, you remove the properties.

Code:

<item href="images/9780399593550_cover.jpg" id="coverimg" media-type="image/jpeg" properties="cover-image"/>

icearch · Yesterday, 09:27 AM

Oh, I actually missed the item herf one. Thanks.

JSWolf · Yesterday, 09:54 AM

Quote:

Originally Posted by icearch

Oh, I actually missed the item herf one. Thanks.

Happy to help.

Put in both so you have ePub2 and ePub3 compatibility.

03-22-2026, 05:31 AM	#1
icearch Zealot Posts: 115 Karma: 1000 Join Date: Nov 2025 Device: none	Epub cover malfunction. How does cover work in epub? I mean, how do software determine what to display as thumb nail? I am being lazy and use a old file to save as a new file to make a new book, since they share same structure. Then I just sawp the cover image in Images folder to a new one, leaving cover.xhtml as it be. Previewing in sigil looks fine, and getting into the book shows cover correctly as well. But thumb nail in reading app becomes random image in the file, or just do not display at all. How does this happen? Where do I left unchageed?

03-22-2026, 07:53 AM	#2
Turtle91 A Hairy Wizard Posts: 3,468 Karma: 21000001 Join Date: Dec 2012 Location: Charleston, SC today Device: iPhone 15/11/X/6/iPad 1,2,Air & Air Pro/Surface Pro/Kindle PW & Fire	Thumbnails are generally handled by the reading device/app so you’d need to follow whatever requirements they impose. Assuming the original epub worked properly and all you did was swap the image, then I would make sure the image references were exactly the same. Something as simple as a capital letter in the file name can cause an error as some software is more strict than others. "Cover.jpg" does not equal "cover.jpg" Also, some software uses the first image in the file list as the thumb. Capital letters can cause the image order to be rearranged. Logo_publisher.jpg could appear before cover.jpg For simplicity and consistency, I make sure to use all lower case letters in image file names and use underscores instead of spaces. I also make sure the cover image comes first alphabetically. In Sigil that is shown by the cover image appearing at the top of the list in the book browser pane. Last edited by Turtle91; 03-22-2026 at 08:05 AM.

Yesterday, 03:05 AM	#4
jugaor Enthusiast Posts: 47 Karma: 17648 Join Date: Jun 2011 Location: Lima, Peru Device: Kindle 10Gen / Kobo Aura HD / Nook STR	Hi, icearch. If you're already using Sigil, you can directly replace the image (without deleting it first) with a new one of the same name. In the following dialog, clicking "Yes" will keep the "Cover Image" property in the new image. [P.S. If you're in a real hurry or using a device without Sigil, opening the epub file with a zip-compressor and replacing the image will achieve the same effect… although it won't pass validation (due to the relocated 'mimetype'), most apps will open it without problems. For a quick personal test, it works. ]

Yesterday, 08:53 AM	#6
JSWolf Resident Curmudgeon Posts: 82,547 Karma: 151278869 Join Date: Nov 2006 Location: Roslindale, Massachusetts Device: Kobo Libra 2, Kobo Aura H2O, PRS-650, PRS-T1, nook STR, PW3	For ePub2 or ePub2 fallback, this is the code in the OPF you use to specify the cover. The top line goes in the metadata. Code: <meta name="cover" content="coverimg"/> For ePub3, you use the following. For ePub2, you remove the properties. Code: <item href="images/9780399593550_cover.jpg" id="coverimg" media-type="image/jpeg" properties="cover-image"/>

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03-22-2026, 08:23 AM	#3
icearch Zealot Posts: 115 Karma: 1000 Join Date: Nov 2025 Device: none	I see the problem. When I deleted the old cover img, <meta name="cover" content="cover-f.jpg" /> was removed in content.opf. After adding that back it becomes normal. The thumbnail software choose is the first pic in alphabet order in Images floder. I created a new clean file and using add cover function in Sigil to observe this. I might consider rename my cover pic to "001-cover.jpg" or something to provide fallback.

Yesterday, 08:42 AM	#5
icearch Zealot Posts: 115 Karma: 1000 Join Date: Nov 2025 Device: none	I see, thanks.

Yesterday, 09:27 AM	#7
icearch Zealot Posts: 115 Karma: 1000 Join Date: Nov 2025 Device: none	Oh, I actually missed the item herf one. Thanks.

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