Since search engines cannot read your image directly, you should help the search engine by adding informations to your img tag.
Here are some tips to make your image search engine friendly:
- Find the right images
- Use the keyword(s) in the file name
- Create descriptive alt text
- The right anchor text
- Make sure the image matches the content

Here is a very recommended HTML code to insert an image.

<img src=""/path/file-name.jpg"" alt="describe your image here"/>