I usually go to www.tinypic.com. Click browse, choose pic, under resize choose forum, click upload. If asked, enter anti-spam code. Then copy and paste forum code here. Pics will be sized correctly and it works well for the smart phones.
I can upload only one at a time using attachments with my iPhone or iPad when online. I need to use my desktop to upload more than one. Otherwise I have to use multiple embedded links from photobucket, etc.