Hi John welcome to TP.
If you look at the bottom of the reply box,
left hand side, you will see "attach files"
Click that and then click the image from your device, and click open.
You then get the option of thumbnail or full size, click full size, and then click post reply at the bottom right hand corner
of the reply box.
If attaching a file direct from your PC / device, into a thread.
this must not exceed 1024px on the longest side or 500Kb
otherwise it will fail to up load.