Follow the questions

In the administration, go to the batch manager and select an album : once you validated the filter, some thumbnails should appear :

• if you get a “No photo in the current set.”, the upload failed : be sure you didn't added to large picture, according to page Photos→Add “20MB. jpeg, png, gif.” for example.
• if you see “XX photos in current set” but just empty squares, read the paragraph 2
• if you see “XX photos in current set” and the thumbnails, read the paragraph 3

Since 2.4, Piwigo has an automatic generation system for thumbnails and other resized pictures. Piwigo call i.php to generate the resized picture in ./_data/i/, then directly calls the resized picture from ./_data/i/. Many problem may appear : an overloading of the server, a picture too big or with a wrong extensions, not enough permission on files/folders etc

1. Checking if an error is returned by the i.php url : right-click on a failed picture then “Display the picture” or “copy the url to the picture”, from your browser. You can also try to display the source code of the page (Ctrl+U usually) and search (Ctrl+F) for an url i.php. Then go to this url with your browser and note any error message displayed.
   1. “source not found” : check by Ftp, if the source picture exists and if the permissions of the file is enough (Chmod : 755 folders 644 files). If it's still not solved, be sure the Php user/system has enough right on your server

If it didn't help you, post on the forum : be polite, write what you did, and add an url to your gallery, Thanks.

Most of cases are permissions issues :

1. Check the level of privacy : in the Batch Manager, click on Edit for a problematic picture. Check the level of privacy, under “Who can see this photo?”. Then go to User→Manage→Properties column and be sure the level of privacy of the users match the one set for the picture. On the Batch Manager, if the picture has a level of privacy different than “Everyone”, it's written right on the thumbnails.
2. Check the visibility of the albums : Go to Album→Properties, and check of the albums are private or not. If there are private, and you did it by mistake, revert them back to public. If not, go to Album→Manage then browse to the album, and then click Edit. Or go to the album on the public part, and click the edit icon. Once you are the edition page, click on the Permission tab : you can see exactly you can see that album, by clicking on “Show Details”. Enable the plugin Multi View, the easiest and fastest way to verify Who Can See What : it opens a pop-up and then select a user in the drop-down list
3. Post on the forum, if the instructions didn't help you