Hmmm, and this isn't the first time.
It's been a struggle to find the right photo hosting site(s) to use. One thing that I really, really appreciate is when folks resize their photos before they upload them; this saves bandwidth, speeds up downloads, etc. The beauty of Postimg is that it allows you to resize when you upload, so it makes it super-easy for folks that don't want to edit their photos before upload.
Personally, I resize and crop all of my photos on my computer, and then I upload to Imgur.com to host them.
I haven't found another free, no-account-required hosting site that will resize like Postimg does.
To do basic resizing and cropping, the
Resizing.app site seems to work well. Go there, scroll down a little, then either drag and drop a photo onto the page or click to search for it. From there, you can crop and then resize; I usually resize by width to 800 pixels.
It will then save the resized photo back to your computer. It won't rotate the photo, so do that before or after if you need to.