IMG

This function convert imageURL into image icon.

So aregisters (in all tables), that contain URL can be converted into images with the help of this function

Try this: No formatting

SELECT i.`KEY` as `Issue`,
it.ICONURL as `Type icon`,
it.NAME as `Type`,
ip.ICONURL as `Priority icon`,
ip.NAME as `Priority`
 FROM ISSUE i
 JOIN ISSUETYPE it on it.ID=i.TYPEID
 JOIN ISSUEPRIORITY ip on ip.ID=i.PRIORITYID
WHERE
   JQL='assignee = currentUser()'

And now Try this: with function IMG

SELECT i.`KEY` as `Issue`,
 IMG(it.ICONURL, 16,16,it.NAME) as `Type`,
 IMG(ip.ICONURL,16,16 ) as `Priority`
 FROM ISSUE i
 JOIN ISSUETYPE it on it.ID=i.TYPEID
 JOIN ISSUEPRIORITY ip on ip.ID=i.PRIORITYID
WHERE
   JQL='assignee = currentUser()'