Follow the questions and instructions Don't understand a technical word? Please Google it or search on the Piwigo Documentation
In the administration, go to the batch manager and select an album : once you have validated the filter, some thumbnails should appear :
Since 2.4, Piwigo has an automatic generation system for thumbnails and other resized pictures. Piwigo calls 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 that is too big or with a wrong extension, not enough permission on files/folders etc
Most cases are permissions issues :
Imagemagick is much more efficient than the GD Graphics Library : less resource consumption on the server and higher quality pictures rendered. Many problem can be solved by changing the graphical library from GD to IM, and your hoster will be glad. Use the following variables with Localfiles Editor :
// Library used for image resizing. Value could be 'auto', 'imagick', // 'ext_imagick' or 'gd'. If value is 'auto', library will be choosen in this // order. If choosen library is not available, another one will be picked up. $conf['graphics_library'] = 'ext_imagick'; // If library used is external installation of ImageMagick ('ext_imagick'), // you can define imagemagick directory. $conf['ext_imagick_dir'] = '/usr/local/bin/';//change with own path!
Ask to your hoster for the path to the Imagemagick binaries.
If this didn't help you, post on the forum : be polite, write what you did, and add an url to your gallery, Thanks.