My pictures thumbnails before upgrade to 2.4 was like this :
But now they use _data/i/thumbnails/...
Is there any way that I can make the thumbnails name like the first one again ?
but they are generated by the system now, not by you (even for FTP direct upload)
I think there is a misunderstanding (from you or me :) )
in Piwigo 2.4 there is only one version of each picture which is persistant : the full-size in galleries or upload
If you want to transfer your pictures from 2.3 (so without keep albums, comments, etc.. right ?) just copy the full-size (in pwg_high if you have one)
previously we had
+--Album +--pwg_high | |-mg_3663.png | |-mg_3664.png | \-mg_3665.png +--thumbnail | |-TN-mg_3663.png | |-TN-mg_3664.png | \-TN-mg_3665.png |--mg_3663.png |--mg_3664.png \--mg_3665.png
now we have
+--Album |--mg_3663.png |--mg_3664.png \--mg_3665.png
so you don't have to worry about thumbnails prefixes, just don't copy them