The Optimus WordPress plugin now allows you to bulk optimize your images. Either via the media library, where you can define which images to optimize or, via Tools -> Optimize all images, where you can optimize all images at once. This feature is available since version 1.3.8.
To bulk optimize images via the media library, select all of the images you would like to optimize from the library view and choose Optimize Images from the drop-down. Then click Apply. This will take you to the optimization page where your selected images will be optimized one-by-one.
The bulk image compression can take quite some time. This is dependent on the amount and size of images. Also the format plays a role. PNG images take much more resources and time than JPEGs. It is important that you do not close or navigate to another site during the optimization process (otherwise it will stop).
A feature to disable the optimization of images upon upload has also been added since version 1.4. This setting is beneficial for users who don’t want to optimize their images right away. This allows users to upload their images as fast as possible, while giving them the ability to later optimize when they have more time. This setting can be toggled by navigating to Settings > Optimus > Optimize during upload.