Sometime you might want to attach a picture as an inline image instead of a regular attachment. To do this in Mailbird simply drag and drop the image to your email. Or click the insert image button at the bottom of Mailbird compose window.
If your inserted inline image is too big or too small, you can adjust it's size right from Mailbird. All you need to do is click on the image until you see a black border like you can see on the image below and then drag the corner of the image to resize.
I hope this help, please contact email@example.com if you are having issue with this feature.