I have a problem, when used import pic. to my database file and upload file on my Dropbox, and download it again in anther PC, I can't found the pic in the database.
Welcome! Can you explain HOW you imported the picture? script? menu? what did the dialog(s) say?
A file/image inserted by reference or with external storage cannot be seen when the file/database is sent somewhere else.
You might research setting up Sharing, so that the other PC can see your database remotely:
I think that you have stored your database externally, not embedded in your file. Then all your files are where you stored your file from the start
Retrieving data ...