I would stay away from any 3rd party file transfer sites. With Gmail any large attachments are sent via Google Drive - it sticks it there, then replaces the email attachment with a link to download.
With Apple Mail it matters if you drag the image into the body, or into the header area (up where the to: & Subject lines). In the header area, it's a separate attachment, where as in the body, you can place it in line - I sometimes do this when writing up directions and steps. If the image is in line, it'll render differently depending on the recipient & their device. If the image is attached, it'll be a click to download type thing.