The GIF format was never designed to be for photos and by definition only allows 256 colours.
From Wikipedia, GIFs are used as follows:
GIFs are suitable for sharp-edged line art (such as logos) with a limited number of colors. This takes advantage of the format's
lossless compression, which favors flat areas of uniform color with
well defined ...
it's year 2019 and I encountered the same problem on iOS 12.4.
Here is how I solved it just now:
Goto Apple ID > iCloud > Photos;
Turn on iCloud Photos. There will be a popup prompting insufficient icloud space;
Press the "upgrade plan" (or something similar, I can't remember the exact words) in the popup, then a new window shows with several icloud plans;
Vector graphics won't help for this kind of task. All your images are in raster format.
Your limit will really be the number of pixels [WxH] rather than 'print size', though you will need at least 150 dpi to print this at a large poster size.
Gimp can apparently save images up to 45,000 x 45,000 pixels [though I can't find citation for this] which should be ...
Photos synced through iTunes won't carry over faces data. Instead, your phone will scan the library manually. It will do this in such a fashion that it doesn't interfere with your battery life.
If you haven't left it plugged in over night you certainly won't see much results
Photos does not reclaim disk spaces immediately after you empty the Recently Deleted folder. Keep Photos opened and allow it to reclaim the disk space. It does take some time. I believe that they are the image caches, thumbnails, indices for searching and all other metadata files being cleaned up in the background. There are a lot of layers to how the photos ...
The less-friction solution would be to upload the compressed version of the photos. And then use iCloud file sharing.
You can try Mail Drop.
With Mail Drop, you can send attachments up to 5 GB in size. You can
send these attachments right from Mail on your Mac, the Mail app on
your iPhone, iPad, or iPod touch, and from iCloud.com on your Mac or
Adobe apps which fit your need according to editing photos or graphic designing.
Canva online editor and app. I haven't used it, but have seen people.