This should do it. Please try with duplicates.
-- Replace Obsidian image links with DEVONthink image links
use AppleScript version "2.4"
use framework "Foundation"
use scripting additions
tell application id "DNtp"
try
set theRecords to selection of think window 1
if theRecords = {} then error "Nothing selected."
repeat with thisRecord in theRecords
set theType to (type of thisRecord) as string
if theType = "markdown" or theType = "«constant Ctypmkdn»" then
set theText to plain text of thisRecord as string
if theText ≠ "" then
set newText to my replaceImageLinks(theText)
if newText ≠ theText and newText ≠ "" and newText ≠ "missing value" then set plain text of thisRecord to newText
end if
end if
end repeat
on error error_message number error_number
if the error_number is not -128 then display alert "DEVONthink" message error_message as warning
end try
end tell
on replaceImageLinks(theText)
try
set ca to a reference to current application
set theString to ca's NSString's stringWithString:theText
set newString to theString's stringByReplacingOccurrencesOfString:("!\\[\\[(.*?)\\]\\]") withString:("") options:(ca's NSRegularExpressionSearch) range:{location:0, |length|:length of theText}
set newText to newString as string
on error error_message number error_number
error number -128
end try
end replaceImageLinks