"HTML Content Support: ability to show websites or other HTML content in a lightbox."..."Automatic Image Detection: configurable automatic re-formatting of image node thumbnails, previews, etc, so there is no need to add 'rel="lightbox"' to each image node link on your site."
Also, imagecache+imagefield+a few other modules work for thumbnailing of images, but they only work for uploads, not external embeds.
My best advice, in that case, is to use CKeditor for comment formatting, since its a WYSIWYG editor with easier user-side options for external embedded image sizing, while also using Lightbox2 for image thumbnail presentation (both external and uploaded). Of course, adding CKeditor may require a bit more comment moderation, as bots could take advantage of CKeditor for spamming the comments section.
According to the page for Lightbox2 on Drupal.org:
Also, imagecache+imagefield+a few other modules work for thumbnailing of images, but they only work for uploads, not external embeds.
My best advice, in that case, is to use CKeditor for comment formatting, since its a WYSIWYG editor with easier user-side options for external embedded image sizing, while also using Lightbox2 for image thumbnail presentation (both external and uploaded). Of course, adding CKeditor may require a bit more comment moderation, as bots could take advantage of CKeditor for spamming the comments section.