Troubleshooting

Start with the question closest to what you are seeing. Every answer suggests a concrete next step.

No image found

The website or extension could not recognize a zoomable image at that address. Check that you pasted the address of the page that shows the image (not an image file itself, not a search page). If it still fails, the site hides its image description file: follow finding the image address, or let the browser extension find it for you.

Forbidden or unauthorized errors

The site sends an error instead of the image. Two different reasons, two remedies:

You normally need to sign in to see this image. The website runs without any sign-in, so the site does not recognize it. Use the browser extension, which works with your own signed-in browser, or get the image address with the extension and send the job to the desktop app.
The site only serves the image to its own pages. Some servers check where a request comes from and refuse everyone else. The desktop app can introduce itself as coming from the site's own viewer page; on the command line, pass -H/--header "Referer: https://the-site.example/its/viewer/page".

Never paste passwords, cookies, or session contents into web forms, chat messages, or bug reports.

The image appears blank, or the browser slows to a halt

Very large pictures can exceed what a browser tab is allowed to hold. The website stops the job with an error and points to the desktop app. Options:

Use the desktop app, which assembles the image in memory (up to its 8 GiB canvas limit, needing matching free memory) and writes the finished output to disk. This is the fix for images that exceed browser limits but fit that cap.
To save a smaller copy, use the command-line tool with --max-width.

The image is visible but the browser cannot save it

Some browsers fail to save very large pictures even when they can display them. Nothing on the website can bypass that browser limit. Use the desktop app, which assembles the image in memory (up to its 8 GiB canvas limit, needing matching free memory) and writes the finished output to disk. The browser extension stays inside the same browser memory and save limits and never fixes this case.

The save stopped partway

Small network interruptions are retried automatically. The tile cache stays on by default, so run the job again and already-saved tiles are reused instead of fetched again (a custom folder uses --tile-cache on the command line): see resuming an interrupted save. If the site changed its image since the first attempt, remove the resume folder and start fresh. On the website, reloading stops the current run; enter the address again to restart it.

The output name is rejected

The output name selects the format: .png saves PNG, .jpg or .jpeg saves JPEG, .tif or .tiff saves TIFF, and a name with no extension saves a IIIF tile folder. Any other extension stops the job before anything is saved. Rename the output to one of the supported forms and run again. A JPEG save of an image larger than 65535 pixels per side also stops with a typed error; save such images as PNG, TIFF, or a IIIF tile folder instead.

The site only works without encryption

A few old sites serve their images without encryption. A secure website is not allowed by your browser to load those. The desktop app can still fetch them: it is an ordinary program on your computer and follows the site's own setup.

The site limited requests from our server

The page could not be opened because the image site limited how often our server may ask. Try again later, or save from your own connection with the browser extension or the desktop app.

The site asks you to wait a few minutes

The image site is receiving too many requests right now. Wait a few minutes and try the same address again.

The image shows but cannot be saved

The site shows the picture without letting Dezoomify save a copy from it. Open the page and use the browser extension to find the image there; see finding the image address.

Sending a signed-in image to another app asks for approval

That approval step is expected. The browser extension asks first before passing anything needed for that job; see what the extension does with your data and the desktop app.

Still stuck?

Disable other browser extensions and try once more; some of them interfere with Dezoomify.
If you believe Dezoomify should support this site, open an issue with the address of the page, the exact error message, and your browser's name and version. A screenshot helps too. Leave out anything private: no passwords, no cookies, no signed-in addresses with tokens in them.

Support is free and done by volunteers; a precise report gets answered much faster.