Re: How do I make sure the photos in my InDesign files are at a high resolution when I send those files to a coworker? (Keeping them as .indd)

Likely when your boss downloads the ID file he is not downloading the images. InDesign will then use the embedded low-resolution preview image. The images need relinked in that case.

Try saving as a packages, upload that folder structure to drop box and have him download that whole folder structure, open the ID file and relink.

Mike