When you apply effects (rotation, shadow, reflection, resample, etc) to an image then Quick 'n Easy Web Builder will create a new version of the image to prevent the original file from being overwritten.
Also if the effect requires (alpha) transparency then it will be published in 24-bit PNG format.
You can specify the prefix of the generated file name in Menu->Tools->Options->Publish
Note: make sure that you do not use the same naming convention for your own images otherwise you may end up with duplicate filenames for different images.