What causes "Cannot copy external images" in Kareadita/Kavita?

Re-package the epub to embed the image as an internal resource instead of an external URL.

Kareadita/Kavita · warning · KavitaException

Cannot copy external images

Error message

Cannot copy external images

What it means

Thrown by BookService.CopyImageToTempFromBook (line 1279) when the resolved image source key starts with 'http', i.e. the image is an external URL rather than an epub-internal resource. Kavita cannot (and will not) fetch remote images during image copy.

Source

Thrown at Kavita.Services/BookService.cs:1279

            var targetImage = images[bookmarkDto.ImageOffset];

            // Get the image source attribute
            var srcAttributeName = GetImageSrcAttributeName(targetImage);

            if (string.IsNullOrEmpty(srcAttributeName))
            {
                throw new KavitaException("Image element does not have a valid source attribute");
            }

            var imageSource = targetImage.Attributes[srcAttributeName].Value;

            // Clean and get the correct key for the image
            var imageKey = CleanContentKeys(GetKeyForImage(book, imageSource));

            // Check if it's an external URL
            if (imageKey.StartsWith("http"))
            {
                throw new KavitaException("Cannot copy external images");
            }

            // Get the image file from the epub

            if (!book.Content.Images.TryGetLocalFileRefByKey(imageKey, out var imageFile))
            {
                throw new KavitaException($"Image file not found in epub: {imageKey}");
            }

            // Read the image content
            var imageContent = await imageFile.ReadContentAsBytesAsync();

            // Determine file extension from the image key or content type
            var extension = Path.GetExtension(imageKey);
            if (string.IsNullOrEmpty(extension))
            {
                // Fallback to determining extension from content type
                extension = imageFile.ContentType switch

View on GitHub (pinned to 9c3e540000)

Solutions

Re-package the epub to embed the image as an internal resource instead of an external URL.
On the client, disable copy-image for pages known to reference remote images.

Example fix

// before
if (imageKey.StartsWith("http"))
    throw new KavitaException("Cannot copy external images");

// caller — pre-check the image source scheme
if (Uri.TryCreate(imageSrc, UriKind.Absolute, out var u) && u.Scheme.StartsWith("http"))
    return BadRequest("External images cannot be copied");

Defensive patterns

Strategy: validation

Validate before calling

// Reject external-image pages before requesting copy
if (Uri.TryCreate(src, UriKind.Absolute, out var u) && (u.Scheme == "http" || u.Scheme == "https"))
    return BadRequest("External images cannot be copied");

Prevention

Re-package epubs to embed images internally rather than hot-linking URLs.
On the client, detect remote src and disable copy-image.

When it happens

Trigger: Bookmark/copy-image request on a page whose <img src> is an absolute http(s) URL to a remote server rather than a path inside the epub.

Common situations: Epubs that hot-link cover art or illustrations from a publisher CDN; DRM/preview epubs with remote-only images.

Related errors

AI-assisted analysis of Kareadita/Kavita@9c3e540000 (2026-08-13). Data as JSON: /api/errors/3e666c85bf7dc6bd. Report an issue: GitHub.