Does someone make a mod that returns the attachment behavior back to how it works in PHPBB2?
Then you said
Not that I am aware of. phpBB3 does not just publish the real address of images for two reasons:
 With the real address, anyone can bypass phpBB3's permission settings.
 With the real address, hacker can try to upload images containing Malware, and try to find exploits to allow them to be executed on your website.
No doubt someone can smuggle a suite case nuclear bomb into the white house too, been using PHPBB2 with the attachment mod since 2003 no problems, only complaints have been on this site, I converted my site from PHPBB2 to PHPBB3 I go into my "files" directory and see all my pictures from the past, I can download them, resize them, reupload them, put them on a DVD mail to friends, now I look at the pictures thats been uploaded since upgrading to V3 and all I see is a file name like 2_71d41923ecc332b883a871bd8bc7aa70 that file is 2.9 megs now I cant download it and resize it I am stuck with that file.
In the past my buddy would run a program on his server and resize all the pictures in the files and thumbs directory this would reduce the size of the directory by a few gigs, saves gigs of me downloading and burning to a DVD for a backup we resized them because no matter what we do or how many times we tell people they still take their 7 mega pixel camera and take pictures then upload they dont know how to resize some do but most forget.
If I wanted to remove a bunch of attachments say all the pictures uploaded to my website in 2010 then put them in my photo album (suggestion from a user) the only way I can see to do this now would be to use a offline website downloader to download EVERY post on my site with attachments so I can get the pictures as a jpg