With Imagick 3.1.0RC2, PHP4.8
If you plan to overwrite the file you're working on, before doing writeImage, consider clearing the file buffer before the write statement :
$image = new Imagick($your_file);
It happened to me that the resulting file size was wrong. This could lead to truncation, as the file is not expanded.
This happened while working on JPEG, and PNG.
this line worked for me without this hack.
Do not rely on getImageLength() for sending your image, especially when keepalive is ON. Content length is then relevant, and must be set. If the wrong size is given, your image will be truncated.
Use filesize($your_file_) once written or strlen($image) instead (which renders your image and updates getImageLength() result).