Evaluate the reliability of a prediction

I don’t really have the labels for the classification, but for every image I have a corresponding array.
Like:
img1, [0.1,0.6,0.8,1.5]
img2, [0.1,0.6,0.68,1.55]
img3, [0.1,0.75,0.8,10.5]

So , finally, the neural network that I trained can give me a array like:
imgTest, [0.3,0.6,0.5,0.9]

I want to evaluate the reliability of the prediction.