After the server migration. The image file has lost I already contact the web hosting service to restore these file. Then I've got the directory of the unknown file type which has exactly the same size of the image attachment file in the file path like this
data\sites\default\storage\000\...
and when randomly open the attachment link the issue with Google Chrome the title show as getattachment.php(703*307 instead of the image file.
How can I restore the image file and make it available as before the server migration?
When doing server migration, you have to copy the entire storage directory to the new server. It contains all the file attachments, and their names correspond to IDs in the database.
Regards,
Michał