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Собственно говоря ... Цитата:

ImageIcon

public ImageIcon(byte[] imageData)
Creates an ImageIcon from an array of bytes which were read from an image file containing a supported image format, such as GIF, JPEG, or (as of 1.3) PNG.
Normally this array is created by reading an image using Class.getResourceAsStream(), but the byte array may also be statically stored in a class . If the resulting
image has a "comment" property that is a string, then the string is used as the description of this icon.

Это собственно говоря как? Константа длиной в n-ное количество кБайт?