I did the plugin according to the instructions. https://docs.ckeditor.com/ckeditor4/latest/guide/plugin_sdk_sample.html I installed a plug-in that they developed the Timestamp, but the picture even does not display their plug-in. http://prntscr.com/j9wzxq http://prntscr.com/j9x078
(CKEditor 4.8.0 (revision 230f715))
Icon name has to match button name in lowercase. Please read the guide carefully one more time.
CKEDITOR.plugins.add( 'pluginname', {
icons: 'buttonname',
...
editor.ui.addButton( 'Buttonname',...
In your case this will be:
CKEDITOR.plugins.add( 'imgcollection', {
icons: 'piccollection',
...
editor.ui.addButton( 'Piccollection',...