I found a way to add multiple pictures to the default mail program on the iPhone.

Compose your email up to the point were you want to insert your picture

Go to your camera roll / photo album (email is saved no worries)

Find the picture you want to include. Hold your finger on the picture and "copy" appears. Tap on copy.

Go back to mail and you will be exactly were you left off. You may then past the image. Rinse and repeat.

When sending the email a menu will pop up and you nay resize the images to reduce the file size