I used DiagTransfer once, and it seemed to work OK, except I think it might have a bug in its FEN string generation (I think it miscounts the move numbers by either a half move or a full move).
There's another program you might want to try, although I haven't used it yet. It's called Chessboard Capture Program:
https://sites.google.com/site/fredm/
I have not noticed any problems with DiagTransfer, but I have not checked the move numbers.
I tried the Chessboard Capture Program, and it works almost in the same way as the DiagTransfer, and it looks like it's still maintained. The DiagTransfer is older, and it looks like it's not maintained any more.
I find it's little more easier to work with DiagTransfer then Chessboard. But both programs do what I want.
No There is no error in the generation by DiagTransfer of "half move) "and "full move number) "The "half move" indicates the number of "half moves" played without the capture of a piece or the advance of a pawn and not the number of half moves played. It is well indicated above "Fifty move draw rule"
"Halfmove Clock"
Informs how many moves both players have made since the last pawn advance or piece capture—known by chess programmers as the number of "halfmoves". This field is useful to enforce the 50-move draw rule. When this counter reaches 100 (allowing each player to make 50 moves), the game ends in a draw."
Alain Blaisot
I uploaded a new version (4.0) last year (August 2021)
Alain Blaisot
Have fun 
I often want to enter chesspositions from the webb to my chessdatabase. But it's troublesome and it's easy to make mistakes.
A usefull tool is DiagTransfer (http://alain.blaisot.free.fr/DiagTransfer/English/home.htm), wich makes this task much easier.
The tool has a transparent board mode wich you lay over the image, and then enter the pieces. When you are ready, you create a copy to the clipboard (in FEN format) which can be pasted to database chessboard.