How to style an image tag in Ruby on Rails
by using "style" option:
<%= image_tag @user.photo.url(:large), :style => "border: 1px solid red" %>
for further info, please check the API.
Add a class or id to your image_tag:
<%= image_tag @user.photo.url(:large), :class => "style_image" %>
Then use css to style it:
.style_image {
border-right: 1px solid #000;
}