How to skip certain code if image does not exist in below code.

EDIT: DOH!  I got my booleans backwards... I've edited the below code a bit... removed the not (!) so that we check for TRUE AND TRUE in the if logic... my bad

The LoadFromFile method returns a boolean value to indicate success or failure to load the image.  So, you need to add some logic around those calls to detect whether or not the method.  This might not be optimal code, but I'd try something like

var baseImage = Utils.Picture
var outputImage = Utils.Picture

if ((baseImage.LoadFromFile(baseImagePath) && (outputImage.LoadFromFile(outputImagePath)) {

diffImage = outputImage.Difference(baseImage);

if (diffImage == null)

Log.Checkpoint('Image comparision passed );
else
{
Log.Error('Image comparision failed)
diffImage.SaveToFile(diffImagePath)
}
}
else {
    Log.Error('One of the images did not successfully load');
}