If you recently upgraded to Wordpress 2.5 and are having difficulty uploading pictures, try putting this in your root directory’s .htaccess file, directly after the “END WordPress”:
<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
This worked for me and I am very grateful. This last version of WP had some very dramatic changes. I’m not thrilled about all of them, but the picture upload issues were my most immediate frustration. Original fix source is here.

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