I don't use Excel much, but I wrote a script a couple of years ago to batch convert Excel files to PDF. You specified as a picture. If you need to convert PDF to another image format, there are Automator workflows around to do that.
The Excel Script (save as a droplet i.e. application):
(* Drag and drop conversion (duplication) of Microsoft Excel files to PDF files using Excel 2008. *)
on open fillist
set bs to "/"
set d to "-"
tell application "Finder"
set defLoc to container of (item 1 of fillist) as alias
end tell
set destn to choose folder with prompt "You are converting (duplicating) Excel files to PDF files" & return & "Select a location to save converted files." default location defLoc
repeat with lvar in fillist
tell application "Finder"
set thename to name of lvar
set filex to name extension of lvar
set l to length of filex
end tell
set nuname to text 1 thru text item -(l + 1) of thename
if "/" is in nuname then
set oldDelims to AppleScript's text item delimiters
set AppleScript's text item delimiters to bs
set txtLst to every text item of nuname as list
set AppleScript's text item delimiters to d
set nuname to txtLst as string
set AppleScript's text item delimiters to oldDelims
end if
set filname to (destn as string) & nuname & "pdf"
tell application "Microsoft Excel"
launch
open lvar
save as active sheet filename filname file format PDF file format
close window 1 saving no
end tell
end repeat
end open