Adding imagesloaded to packery module
Super late but support for this request has been added in the latest commit of the Packery module: Commit 24856cf on 7.x-1.x by swim: Added imagesLoaded support on per settings basis.

Just toggle on/off on the settings page, and read the README.txt for the plugin placement. Here is a quote from the updated README.txt:


  ImagesLoaded support
  
  For imagesLoaded support please download the plugin from https://github.com/desandro/imagesloaded.
  Place the plugin in the libraries directory at sites/all/libraries/imagesloaded so that the file is at sites/all/libraries/imagesloaded/imagesloaded.pkgd.min.js.