Pues buena pregunta , nunca me la habia planteao la verdad, buscando un poco en el Faq que viene en la página puedes ver esto:
12. would like an image to be deleted. What do I do?
Generally, it is not necessary to delete a picture that you no longer have use for, or one that you accidentally upload. This is because ImageShack(TM) has enough harddrive space to accomodate your needs, and then some. However, If your image or any image that you find violates the Terms of Service, please report it by Contacting Us. You will also be able to delete your own images if you Register an Account.
Mi ingles es very patatero, pero vamos creo que no vas a poder, lo que podrias hacerlo si te registras , entones te dan un codigo o algo de todsa tus fotos subidas y tu te las administras.
Pero vamos ni idea eh , es mas o menos leyendo por encima.
saludos