Swap all images to existing slims
Replaces original images with slimmed (optimised) versions.
Click Swap all images back to existing slims to replace the originals images in an InDesign document with previously created optimised copies of those images.
The scaling and placement of the images is retained. You can check the Links panel to verify that the images have been swapped.
In InDesign you can elect to view an additional column in the Links panel to check the Effective PPI of images within the document:
To add the column choose InDesign Window menu > Links > Panel Options from the panel menu: