With Akeeba Backup Core you have to manually exclude the Thumbs.db files using the Files and Directories filter. With Akeeba Backup Professional you can use the RegEx Files and Directories Filters page to add "Thumbs.db" as a global filter. As soon as you do that, all those files will be skipped from the backup set.
Alternatively, you can extract using Akeeba eXtract Wizard with "Ignore most errors" turned on. This will eliminate the errors when trying to unpack the Thumbs.db files.
Nicholas K. Dionysopoulos
Lead Developer and Director
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