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The first thing that comes to your mind is probably TImage.Picture.Free but I wouldn't recommend this :-) Not only will this actually empty the image but also free the memory associated with it. Uhm... What does this mean? That you will no longer be able to access the TImage.Picture object. It will no longer exist, it'll be gone (*puff*). The solution is more than simple:

    Image1.Picture := nil;