Fresh install. V3.2.3Pro. Call /amember/captcha.php gives error message: /amember/includes/kcaptcha/fonts/bookman.png' is not a valid PNG file. File indeed is corrupt. Re-uploaded folder /amember/includes/kcaptcha/fonts in automatic FTP mode (not binary mode). Seems to work here. PS during FTP uploading of the Amember script to the server the communication failed and had to resume. Maybe that has something to do with corrupting the files?
@pkrpkram: I'd suggest uploading the .zip file and unzipping locally on the server. This would eliminate any binary/test/automatic upload issues.