We all noticed that Joomla html editors (whatever it may be - TinyMce - the default one, or JCE) are replacing the absolute path of images (whether they are http://www.... or /images/...).
The image URL is always saved as "images/my_folder/my-picture.jpg" (relative path).

This is okay if we do not install Joomfish in Joomla which will display our articles with custom paths. These custom paths from the links are messing the images if they use the default paths (as they are saved by Joomla editors). We will not see the images, but just the ALT tag of the images instead. A workaround is to disable the HTML Editor from Site - Global Configuration and put the absolute path in the article. But this is difficult, since we are "reading" HTML code.
The solution is simple, all you need to do is set the Plugin - System SEF to Enabled. Images will be saved as before, just that they will now properly display in the frontend.
That's it.

