Abstracts for CHC 2018 were published on September 17. However, authors are still able to upload copies of their posters in PNG format to be used as TOC images and in PDF format to be uploaded as Multimedia Appendices.
Simply go to http://www.iproc.org/author/submission/##### (and replace ##### with your four- or five-digit manuscript ID) and click "Add a Supplementary File". Note that adding new files this way will notify JMIR staff so that they can ensure that the published version of your abstract is updated to include the PDF of your poster.
Note: Post-publication file uploading is not permitted for any article published outside of iProceedings.