Vrftjkry

Here's a way using PowerShell:

Navigate to your folder and run this command

Get-ChildItem *.jpg | Rename-Item -newname {"._" + $_.Name}

Extra bonus short version:

gci *.jpg | ren -newname {"._" + $_.Name}

I have 2 solutions:

1. 
   

   All files are in the same folder

   
   
   
   
   
   • 
     

     run the following from command prompt on that folder:

     
     
     

     for /f "delims=¯" %i in ('dir /b /on') do ren "%i" "._%i"
     
     

     
     
   
   
   
   


2. 
   

   complete solution when there are files in subfolders AND when you wanna to replace the "n" first characters with a string you want :D

   
   
   
   
   
   • create a batch file with the following command
   
   
   • change variable parameters to what you want
     
     
     
     
     • 
       path: put inside "" the root path of your files (e.g. "C:documents and settingsuserdesktopnew folder"
     
     
     • 
       numfirstchars2replace: put a number with the first characters to replace (in your case, 2)
     
     
     • 
       str2put: put a string to be added as a prefix of the new filename (in your case, ._)
     
     
     
     
   
   
   • run it in a folder different from where the files are
   
   
   
   

@echo off



::only to tell user what this bat are doing

echo.1.initializing...



::enable that thing to allow, for example, incremental counter in a for loop :)

echo.- EnableDelayedExpansion

SETLOCAL EnableDelayedExpansion



::variables

echo.- variables

:: - place here the absolute root path of your files

set path="put here where are the root folder of your files"

set pathbak=%cd%

set numfirstchars2replace=2

set str2put=._



::go to %path% and its driveletter

echo.- entering the path you want

for /f "delims=¯" %%i in ('echo.%path%') do %%~di

cd %path%



::search all subfolders and save them to a temp file

echo.- searching for subfolders

echo.%path%>%temp%tmpvar.txt

for /f "delims=¯" %%i in ('dir /s /b /on /ad') do echo."%%i">>%temp%tmpvar.txt



::execute command for root folder and all found subfolders

echo.

echo.2.executing...

for /f "delims=¯" %%i in (%temp%tmpvar.txt) do (

  cd %%i

  echo.- in folder: %%i

  for /f "delims=¯" %%j in ('dir /b /on /a-d') do (

    set newname=%%j

    set newname=!newname:~%numfirstchars2replace%,1000!

    echo.- renaming from "%%j" to "%str2put%!newname!"...

    ren "%%j" "%str2put%!newname!"

  )

)



echo.

echo.3.exiting...

::return to %pathbak% and its driveletter

for /f "delims=¯" %%i in ('echo.%pathbak%') do %%~di

cd %pathbak%



@echo on

If they are all in the same folder, you could select them all with Control + A and then hit F2 to rename one of them. All subsequent files will be named file(2), file(3), etc

Try Powershell (preinstalled in Windows 7):

Get-Childitem /path/to/your/files | foreach-object { move-item $_ $("._" + $_.name) }

(tested it in my download-dir.)

Edit: Siim K's code will append an additional ".jpg" to every "._filename.jpg".
Remove that last ".jpg" in Siim K's code and you have a short, elegant code to rename your files.

Total Commander has a really nice multi-renaming tool.

I've always found Flash Renamer to be a good tool for renaming files in batches.

It has trial and full versions ($20) and can rename files based on meta data - very useful for renaming MP3 files which I what I use it for mostly.

If your looking for a user friendly way of renaming in bulk you could try the free tool Ant Renamer, there's a huge list of actions you can take and it also gives a handy preview before you do any renaming. I use it a lot when messing with my music, photo or video librarys.

I have used this freeware File Renamer program with great results. Many different filters and options, plus it gives you the ability to test results. A little outdated UI perhaps but works like a champ.

http://www.webxpace.com/software/freeware.shtml#FileRenamer