Hi Doc2018,
I'm a fellow Weebly User. One way around this is to do a bulk upload of your full-size images in your file manager.
To do this in the Weebly Editor go to Theme (in the top menu), then along the left-hand side of the editor you'll see a button at the bottom that says Edit HTML/CSS. Click that, then in the "Assets" folder click the + sign and select New Folder. Name your new folder, then click the gear icon next to it and click "Upload Files" You can then upload a single photo or do a bulk-upload of any and all images.
These images will all be available in full-resolution. Next, go back to the site builder, add smaller versions of the images to your page and link the images to the full size files, having the link open a new window with the image file.
The URL will be based on the folder you created and the file name. So for example your link might point to:
https://www.yourdomain.com/files/theme/foldername/image-file-name.jpg
Obviously you'll update https or http depending upon your site protocol.
In this way you can organize all of your image files in different folders too. Say /files/theme/images/file-name.jpg, /files/theme/headshots/file-name.jpg, etc.
If you have a ton of images you're uploading, I recommend keeping a database of the image file names and URLs in Google Sheets or something, so you can quickly find and add the appropriate link anywhere on the site.
Of course you can also embed the photos in the page with a custom html block in this way, but your site will load faster by uploading smaller versions of each image using the "Image" widget in the editor.
Hopefully this helps you. 
Good luck!
