In this animated GIF, an advert for Lexus, we see a call to action which says "Click Here".

Lexus Advert

Would it not be obvious to readers that this is an advert? That adverts are clickable?

Perhaps not. Let's see how it is laid out on Reuters Mobile.

Advert on the Reuters Mobile site

Utterly bizarrely, this image isn't clickable! The user will try in vain to click where it says "Click Here" and get nowhere - they have click on the word Lexus.

Take a look at the source code, if you don't believe me.

HTML Source Code

Make Your Advert Easy To Access

Seems obvious, no? The bigger the target area, the more chance a user will be able to click on it. This is a big usability issue - especially on phones touchscreens, trackpads and rollerballs.

We see this issue in HTML forms as well. In this example, it's easy to select the "Male" option simply because the label is clickable.

The "Female" option is harder because you need to have the dexterity to accurately position your cursor over the tiny radio button as opposed to a larger target.

For a chance to win an AMAZING prize - click this dot . It's not the easiest thing in the world. Especially on a mobile device where the cursor may only move in large steps.

What To Do?

Having a hyperlinked word or phrase under an advert certainly isn't going to hurt.  When it's the only way to access the content, you risk confusing your users' mental model about how images work.

Above all, never say "Click Here" if there's nowhere to click.