Cambiar tamaño, peso, de una imagen

[mdk]

Sustituyendolo me da todos estos errores:

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<b>Warning</b>: imagecreatefromjpeg: Unable to open 'ÿØÿà' for reading in <b>d:\web\fotos-irc\users\foto.php</b> on line <b>12</b><br />
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<b>Warning</b>: imagesx(): supplied argument is not a valid Image resource in <b>d:\web\fotos-irc\users\foto.php</b> on line <b>16</b><br />
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<b>Warning</b>: imagesy(): supplied argument is not a valid Image resource in <b>d:\web\fotos-irc\users\foto.php</b> on line <b>17</b><br />
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<b>Warning</b>: Division by zero in <b>d:\web\fotos-irc\users\foto.php</b> on line <b>19</b><br />
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<b>Warning</b>: imagesx(): supplied argument is not a valid Image resource in <b>d:\web\fotos-irc\users\foto.php</b> on line <b>26</b><br />
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<b>Warning</b>: imagesy(): supplied argument is not a valid Image resource in <b>d:\web\fotos-irc\users\foto.php</b> on line <b>26</b><br />
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<b>Warning</b>: imagecopyresized(): supplied argument is not a valid Image resource in <b>d:\web\fotos-irc\users\foto.php</b> on line <b>26</b><br />