Currently Slack doesn't support rich text editing in their dialogs. For links, if you include the entire qualified URL, Slack will attempt to parse it when the report is posted and if a valid link is found, it will create the link. For images, the current workaround is to reply to your report in the standup channel with any relevant images you would like to reference from your report.
Here is an example on how you could reply to your standup to add additional context: