After bug 162527's fix, attachment 195910 [details] and attachment 205053 [details] correctly hide the images when opened, and when saved back to DOCX. Save them to ODT instead, and reopen. => The images are shown in each document. Interestingly, with shapes this is now OK, saving attachment 204398 [details] from bug 169802 as ODT and reopening it correctly hides the shape. Observed using LO 26.8.0.0.alpha0+ (840c354ed653174002cf42a44b9ab4dcb9b55ecc) / Windows.
Note that there's no way to hide an image in Writer UI.