You could try the SNDDST command, specifying the following parameters:
TYPE = *LMSG – long message
TOINTNET = email address – this address must be in the directory list. (Press F1 to read about it).
SUBJECT = 60 chars max
LONGMSG = The body email content
I think you can put html code into LONGMSG parameter, and maybe include the image, encoding it to Base64 (google for “embedding images in html” to see how to do that).
Another way is to write a Java application that uses the Java mail API to send emails, and call it from RPG code. To use java classes from RPG read this http://publib.boulder.ibm.com/infocenter/iadthelp/v6r0/index.jsp?topic=/com.ibm.etools.iseries.pgmgd.doc/c0925076172.htm