I'm certainly no IT expert, but I do the following to get my photos posted here: I use the "Batch Processing" function of Adobe Photoshop Elements to resize a group of photos to 800 by 800 pixels maximum. Make sure that you constrain the ratio, so it does not stretch or compress one axis of the photo. I upload the resized photos to my Photobucket account, from which their unique "address" can by copy and pasted into the dialog box you get when you select the insert image icon in the tools above. Sometimes it can fiddly, so check what you've uploaded to see it is what you intended. Note that photos exceeding 800 pixels in any dimension will cause the PPRuNe pages to be buggered up. Photobucket can also be used to resize, but I have found this challenging, with my modest website skills....
Let's have some photos of where other PPRuNe members fly... I'll put up some more later....