The DUP used the model for a poster attacking the Tories
It has emerged that two unionist parties who used a stock photo of the same model in rival election materials may have breached the terms and conditions for using the pictures.
The stock photography company which licenses the pictures, istockphoto, told the BBC it is investigating the matter.
The DUP first used a picture of the model next to a slogan reading "I'm voting DUP".
In a retaliatory move UCU licensed another picture of the same model with text saying she had changed her mind and would vote for them instead.
The list of terms and conditions on the istockphoto website states these pictures cannot be used in a way that "depicts personal endorsement by model".
The UCU created another poster using a picture of the same model
It specifies that it is prohibited to use models in such a way that it would lead "a reasonable person" to think the model personally endorses any cause.
The only exception is where the picture is accompanied by a statement that explains the content is being used for illustrative purposes only and that the person depicted is a model.
A spokeswoman for istockphoto said: "We care deeply about the correct usage of the images licensed on our site and our compliance team will be investigating this matter, as it does others such as this."
She suggested the parties may not have been aware they could have been breaching the terms saying "we caution against a blanket assumption of malicious intent".
However, she said anyone using the company's service should be aware of the rules.
"People really should read carefully the terms of service on any contract they sign, or checkbox they tick off."
An Ulster Conservatives and Unionists spokesperson said: "Our 'spoof' poster is being used for illustrative purposes only, with no intention to reproduce on a billboard.
"We are of course aware that the person depicted in the content is a model - indeed the point of our poster was to highlight that very fact. This was made clear to recipients."