Thinking the uneven heat was “odd” compared to other people, Ms Gill carried out an internet search on thermal imaging cameras and found out they can be used by oncologists to help diagnose cancers.
The 41-year-old, from Slough in Berkshire, was diagnosed with breast cancer at the “really early stages” and is now waiting for a third operation to try to prevent the disease from spreading.
She has now contacted the visitor attraction on the Royal Mile to tell them “how my visit to the Camera Obscura changed my life”.
In a letter to the Camera Obscura & World of Illusions, Ms Gill wrote: “While making our way through the floors we got to the thermal imaging camera room.
“As all families do, we entered and started to wave our arms and look at the images created.
“While doing this, I noticed a heat patch (red in colour) coming from my left breast.
“We thought it was odd and having looked at everyone else they didn’t have the same.
“I took a picture and we carried on and enjoyed the rest of the museum.”
For me it really was a life-changing visit. I cannot tell you enough about how my visit to the Camera Obscura changed my life
She added: “A few days later when we returned home I was flicking through my pictures and I saw the image.
“At this point, I searched on Google to see what this could mean and I saw a lot of articles about breast cancer and thermal imaging cameras.
“I made an appointment with the doctor and as it turns out I do have breast cancer, thankfully really early stages.
“I have now had two surgeries and have one to go to prevent it from spreading.
“I just wanted to say thank you – without that camera I would never have known.
“I know it’s not the intention of the camera but for me it really was a life-changing visit.
“I cannot tell you enough about how my visit to the Camera Obscura changed my life.”
General manager Andrew Johnson said: “We did not realise that our thermal camera had the potential to detect life-changing symptoms in this way.
“We were really moved when Bal contacted us to share her story as breast cancer is very close to home for me and a number of our team.
“It’s amazing that Bal noticed the difference in the image and, crucially, acted on it promptly.
“We wish her all the best with her recovery and hope to meet her and her family in the future.”