size of database get smaller after deleting blobs ?

[benja]

hi,
i have a big database witch contains JPGs stored.
The database is 100 GB (2 million rows aprox), on an 120 GB Hard Disk Drive.

I want to backup by parts dumping gradually those JPGs to filesystem and then to DVD.

Does the database get smaller in size every time i delete rows ? Or only when an maintainance script is executed ?

Can the database run a maintance process with only the 20GB free ? does it copy itself before doing this ? Will the optimize procedure fill de disk before completing ?

Tables are MyISAM.

Any Advice ?

Thanks in advance.