Broken b64 decoding

Could it be due to there are '\r' characters in your base64? What about trying to remove it in step 4:

 

 

tr -d '\n|\r' < file_with_newlines > file_without_newlines

 

 

Or, try to verify your base64 in LTM (eg. file_with_newlines):

 

 

openssl enc -d -base64 -in file_with_newlines -out file.png