Attach pictures to sales invoice - several pictures at once.

Hi there, I have been attaching images in sales invoices in the Attachment section of the Invoice record, it takes time to do but in the long run when we have more images then one.

Question:  When attaching the Images I have to do them one at a time as I cannot highlight more than one at a time, am I doing something wrong and there is a way to do it or is it one at a time and that's it? Is any solution to modify way to attach several pictures at once to the invoice.