A customer who was emailed the photo said the model looks "unhealthily thin" in the long blue dress and accused the store of being socially irresponsible.
But, Selfridges is now being backed by the Advertising Standards Authority (ASA) which concluded that the model was not unhealthily thin and the advert wasn't irresponsible.
Agreeing with previous comments by Selfridges, the ASA's assessment said: "The ASA acknowledged that while the image did emphasise the model's slenderness through pose and the style of clothing, she appeared to be in proportion.
"We considered most people, including young children and women, would interpret the ad as focusing on the design and fit of the dress, rather than on desirable body image".
Liam Preston oversees the Be Real body image campaign which is part of the Christian youth charity, YMCA.
He tells Premier such images can be harmful: "I think their current regulations possibly aren't fit for the purpose for what we're seeing.
"They do need to take a stronger look on the damaging effects that some images have. The one from Selfridges isn't helpful but it is my no means the worst out there".
The Be Real Campaign works with several retailers including Dove and New Look.
Preston tells Premier projecting positive body image should be a priority for retailers: "From a consumer's perspective, the maths is simple.
"If you see a model or advertising that look similar to what you look like, you're more likely to buy that product so it's also in the interest of retailers to come on board with what we're saying as well."