Snippets do not include attachments by default, but there are ways around this for images. You can add inline images by using Gmail's Web Address (URL) option in tandem with your snippet.
- Open a new Compose window
- Click the Insert Photo button from the toolbar at the bottom of the window
- Select the Web Address (URL) tab and paste the URL into the input form.
- Confirm by clicking Insert.
Need image hosting?
If you don't have your own content delivery network, you can utilize Google Drive for image hosting purposes via Doc.
- Open Google Docs and create a new document and give it a name like "Images for Emails"
- In the top right corner of the Google Docs interface, click the Share button.
- From the sharing window, select Advanced
- Under Who has access click Change... from the right column.
- Select On - Anyone with the link and confirm the change by clicking Save
- Insert the image into the Google Doc
- Select the image and copy it from the Google Doc and paste it into the Compose window.
As long as the Google Doc is not deleted from your Google Drive, the image will always be accessible and will display properly when sent.