4
In your myAlbum-P admin menus you got 'Rebuild Thumbnails' - that's what you need. Before it, in your module Preferencies you have to choose the php module for building thumbs - GD / ImageMagic / NetPBM, and also you have to turn the option of making thumbnails on. As panigrc said, call the phpinfo() function on your server or use the 'XoopsInfo' module to see it there - the information if and which of them you got installed. From the 'Check Confs&Envs' myAlbum-P menu you can see some info and check if the choosen package is working ok. Then go to 'Rebuild Thumbnails' and follow the instructions there, so thumbnails will be built for the existing images and for the next uploaded images they will be created automatically.
Good luck!