Dear what is the size of your feature vector, if it is column vector then let say your have 1000 feature vector of 1000 images. I denote it by D, where each column is feature vector of each image, in short column represent single image. and your Query image is Q is single column vector.
it can be computed as simple as;
E_distance = sqrt(sum((Q-D).^2));
now E_distance is euclidean matrix distance. where each cell is distance of Query with database image.