As seen on Bitnami’s forums: https://community.bitnami.com/t/permission-issue-could-not-upload-images-to-wp-content-uploads/30664

Connect to your site via ssh.

Then check the uploads directory permissions.

ls -l /opt/bitnami/apps/wordpress/htdocs/wp-content/uploads

Then user the Bitnami user to fix permissions if necessary

sudo chown -R bitnami:daemon /opt/bitnami/apps/wordpress/htdocs/wp-content/uploads/