Copy and paste?

[Quarterpoundher]

Don’t give up Rover you’re nearly at the…

[El Gordo]

When you're composing your reply there should be a section further down the page titled Additional Options with a button labeled Manage Attachments. Click it and a window will pop up. You can browse for files from your computer, or you can type in the address of the file on whatever website you want to take it from. The window will list the maximum allowed sizes. If the image is too big then you will need to resize it, but that's more complicated.