Gimp is a good free downloadable photo editor...similar to photoshop, but not near as pricey. Otherwise I use photobucket, you can set the size you want and it will automatically resize when uploaded, there are aps to upload from Apple or Android devices or if you don't have such a fancy device, you can email to upload from other phones. Copy and past the IMG code into your text and post as many photos in a row as you want...actually, make them i a column, I hate it when people put photos side by side and you have to scroll to the right to see everything. (Just put a carrage return or two between the IMG codes when posting multipel pics.
Chuck