use scripting additions
use framework "Foundation"
use framework "AppKit"
on convertPICTFileAt:posixPath
-- build new path
set oldPath to current application's NSString's stringWithString:posixPath
set newPath to oldPath's stringByDeletingPathExtension()'s stringByAppendingPathExtension:"jpg"
-- make NSImage from file
set theImage to current application's NSImage's alloc()'s initWithContentsOfFile:oldPath
-- get TIFF version as data
set theData to theImage's TIFFRepresentation()
-- make bitmap representation from TIFF data
set bitmapImageRep to current application's NSBitmapImageRep's imageRepWithData:theData
-- extract jpeg representation from bitmap
set theData to bitmapImageRep's representationUsingType:(current application's NSJPEGFileType) |properties|:{NSImageCompressionFactor:1.0} -- between 0.0 and 1.0
--save to file
theData's writeToFile:newPath atomically:true
end convertPICTFileAt:
You'll need to save it to a script library under Mavericks.