Images can only be inserted into the body of an email sent using the HTML format, not in 'plain text' emails. Further, they can only be seen within the body of the text by someone with their email settings configured to use the HTML format. (So, even if you send an image embedded into the text, the person receiving the email might get the image appended as an attachment, which he/she needs to open, because they're using the 'plain text' setting).
You've not told us how you're sending your mail. (Are you using a dedicated email client, such as Outlook Express, Windows Live Mail, Windows 10 Mail or Thunderbird? Or are you using a web-based system? They're all different!). However my guess is that you've got 'plain text' in use, rather than 'HTML'. (If you need instructions on how to change that we'll need to know how you send your emails).
It's worth noting though that many people have 'HTML' disabled in their email clients, as it's considered to present a security risk, so (as I've indicated above) recipients of your emails might well not see your images embedded in the mail you send anyway.