dezoomify-rs can be used to download a full resolution image from easyzoom.com when the author has disabled the download button. Here are the steps that worked for me on Windows Chrome:

1. In the browser window that contains your zoomable image, open Chrome's Developer Tools pane (press F12).
2. Under the Network tab, select Fetch/XHR.
3. Look for a 1-2kB XHR file with a string of 32 random characters for its name. Select it.
4. Near the bottom of the file's content you'll find a node named TilesZipUrl. Its value is a URL for an szi file. Copy this URL and paste it into a new browser tab.
5. The tab will take a while to download the szi file, then will display it as an icon on a black background. Right-click the icon and select "Save As..." to save it to disk.
6. Once downloaded to disk, rename the file to end with .zip.
7. Extract the zip file to disk. Find a dzi file within the extracted location.
8. Download the latest version of dezoomify-rs.exe here: https://github.com/lovasoa/dezoomify-rs/releases
9. Execute dezoomify-rs.exe from the Windows command line.
10. Paste the path to the dzi file extracted in step 7. For example, C:\0b29f1a2-41fa-4f60-9e8b-f435405dee88\0b29f1a2-41fa-4f60-9e8b-f435405dee88.dzi
11. Enter the zoom level you wish to "dezoomify" (0 for the full resolution).
12. A file named dezoomified.jpg will be saved to disk that contains the full resolution image.