Absolutely no experience with resizing on an iPad. Highly recommend registering (free) at Photobucket.com (they even have an app, although I've only used the desktop version). I've uploaded at least 150 images there and it shows I've used 3% of my available, free space. It has some nice editing features and linking to an image there will also help the space required at any forum where you 'post' an image; the space used is at Photobucket, not the forums.
I'm now investigating the app on my iPhone. If I can do something
there, the iPad should be a snap!
It does have ads along the bottom of the screen... but most 'free' apps do.
I see your 'selfie'. That size is fine with me, even though I have to scroll sideways a bit. I keep my browser window at only 1200 x 900 pixels, normally. I also have1000 x 800 and even an 800 x 600 pixel rectangles on my home page. It helps me make sure any web page I create will fit even older computers!
The problem is that most forum software has a column or two on the sides of their pages which means images displayed in a post won't be able to use the whole width of the browser window. Really old forum software will even cause the entire page to stretch to display those wide images and then every post also becomes that wide forcing viewers to scroll horizontally just to read any post, even the ones without images!
Fortunately that's not the case here.
I hope you have some mattresses or even a trampoline on that deck behind you... a good healthy gust and you could be 'testing' them out!