How to use Euclidean Filtering for object identification in an image

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C#

I was suggested to use Euclidean filtering to identify object in an image.
But on working with it, I realized that while applying the filtering on an image, the whole image except very little portions of it turns black. But i had expected the background to turn black and the object in it to remain unaltered.
Is there any other way to identify object in an image like finding the contrast or the energy or something like that for the two images and then comparing the difference, or something like that?