Use a private instance of sorl.thumbnails.

wiki/plugins/images/templates/wiki/plugins/images/index.html

 {% extends "wiki/article.html" %}
-{% load wiki_tags i18n humanize thumbnail %}
+{% load wiki_tags i18n humanize wiki_thumbnails %}
 {% load url from future %}
 
 {% block wiki_pagetitle %}{% trans "Images" %}: {{ article.current_revision.title }}{% endblock %}

wiki/plugins/images/templates/wiki/plugins/images/purge.html

 {% extends "wiki/article.html" %}
-{% load wiki_tags i18n humanize thumbnail %}
+{% load wiki_tags i18n humanize wiki_thumbnails %}
 {% load url from future %}
 
 {% block wiki_pagetitle %}{% trans "Purge deletion" %}: {{ image }}{% endblock %}

wiki/plugins/images/templates/wiki/plugins/images/render.html

-{% load thumbnail i18n %}{% comment %}
+{% load wiki_thumbnails i18n %}{% comment %}
   This template is used for the markdown extension that renders images and captions.
   
   NB! Watch out for line breaks, markdown might add <br />s and <p>s.

wiki/plugins/images/templates/wiki/plugins/images/revision_add.html

 {% extends "wiki/article.html" %}
-{% load wiki_tags i18n humanize thumbnail %}
+{% load wiki_tags i18n humanize wiki_thumbnails %}
 {% load url from future %}
 
 {% block wiki_pagetitle %}{% trans "Replace image" %}: {{ image }}{% endblock %}

wiki/plugins/images/templates/wiki/plugins/images/sidebar.html

-{% load i18n wiki_tags wiki_images_tags humanize thumbnail sekizai_tags %}
+{% load i18n wiki_tags wiki_images_tags humanize wiki_thumbnails sekizai_tags %}
 {% load url from future %}
 
 {% addtoblock "js" %}

wiki/plugins/images/templatetags/wiki_thumbnails.py

+from sorl.thumbnail.templatetags.thumbnail import register