You don't need to write it to a file, just use -count of strings- on your regexp. It's only one medium complex macro then.
Edit: Just tried, it's like that:
{-String.SplitCount-|-{-RegExp.RegExp-|-{-File.GetBlock-|-\_projects\stuff.txt-|--|-0-|-false-}-|-(?<=I\/)[\w\W]*?(?=\.jpg)-|-all-}-|-{-String.Enter-}-}
What it does:
{-File.GetBlock-|-\_projects\stuff.txt-|--|-0-|-false-}
Gets your raw data
{-RegExp.RegExp-|-RAWDATA-|-(?<=I\/)[\w\W]*?(?=\.jpg)-|-all-}
Get me a list of jpgs, everything from rawdata that looks like that: 'i/*******.jpg'
{-String.SplitCount-|-LISTofJPGS-|-{-String.Enter-}-}
Count the amount of entries, delimiter is linefeed(enter)
All in one go.