On Ipad, you don't have a "windows explorer app" (for obvious reasons) but you can still upload images using the upload icon. Select it and you will get a dialog that asks if you want to upload an image from your device or from a URL. Choose the device if that's where your photo is.
The upload icon is illustrated here: it is the horizontal bar with the upward arrow in the toolbar seen when you are editing an item. I created this image just now from a screenshot on my Ipad, used standard ipad pic editing tools to crop and then markup the clip. Finally used the upload button to upload the edited pic. (On the ipad)
I dare say if you were on windows or OSX you would get a similar dialog if you click the same upload icon. [Edit: just checked on windows and yes, click that icon and you get a dialog asking you what file you want to upload]
Hope this helps.
73 Andrew VK1DA VK2UH