I am working on a CartoDB-map where I want to display my readers' photos of the fish they have caught this summer.
I have added an image url to each row in the table, dragged it to the top of the infowindow display list, enabled it and changed the image window type to Image Header.
It displays nicely in the editor, but when I view or embed the map, the tag has the css style display:none; attached to it as a style property.
Even when I manually add display:block; or display:inline in the CartoDB infowindow HTML editor.
(This solves the problem if I do it in the Chrome or Firefox developer consoles).
Public map: http://kjethoe.cartodb.com/viz/50b0eafc-3b54-11e5-be03-0e0c41326911/public_map Final usage: http://interaktiv.gd.no/2015/fiske/?v=a
Unfortunately there is a problem in CartoDB.js that hides the image (if exists) within the infowindow header in order to create the new one using the first column available in the internal fields list.
While issue is fixed, I encourage you to rename the column that has url images to '_whatever'. This will make that column to be the first available column within the internal fields, and it will be rendered properly in the infowindow despite of this problem.
Let me know if it solves the problem.