Well if (something) is all the pattern you can provide for us then really the only regex match I can think of is .*. However based on your description I can't tell if you have parantheses in the filenames or not. I'll give you a regex for each situation.

if (/\<img src=\((.*)\)-disclose\.gif.*\>/i) { $_ = "" }
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That will work if the filenames have parantheses. The following will work if they do not:

if (/\<img src=\(.*\)-disclose\.gif.*\>/i) { $_ = "" }
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After the regular expression the variable $1 will contain the name between (something). (ie: print "$1-diclose.gif\n"; will give you the filename)
WARNING: the regexp's are untested but should give you the idea! (in a regex putting a match between () assigns the variables $1,$2,$3...)

-Adam Stanley
Nethosters, Inc.