“Phupp”, in the Apple App Store, makes it very convenient to upload photos from iPhone Photos to ImageShack. You can select reduced resolution uploads, but that’s scarcely needed for ImageShack, unless you need to reduce upload bandwidth usage. The app appears to be dedicated to the ImageShack hosting site, but might work for others – haven’t investigated.

The app is stable, and actively maintained, with a several-year history and a fairly recent revision. It’s free, with a 99¢ in-app “no ads” offer. I don’t recall ever seeing an ad, but might pay the 99¢ anyway, to reward the developer for this sweet little app.