Compressed code:

```ruby
<% if a.type.eql? "TwitterAuthor" %>
<%= link_to (image_tag "pastel-tw.png"), " " %> 
<% else a.type.eql? "TumblrAuthor" %>
<%= link_to (image_tag "pastel-tumblr.png"), " " %> 
<% end %>
```
Indenting aside ;) ..this sort of if/else condition based on the *type* of the object is usually an indication that you really want to have a method on each Object, that does something different.  That is to say, you have a TwitterAuthor and a TumblrAuthor class, so rather than doing this kind of switching, I'd suggest adding a ```service_image_link``` method to each of those classes (along with a nice default for the Author class they inherit from..)- then you only have to do this in your view:

```ruby
<%= a.service_image_link %>
```

Much simpler!