is there option to use image links instead of uploading pictures to site?

Currently the only way to add images is to upload them with each Ad.

Why? They can add these picture links in ad description but why they are not allowed use outside picture URL to show ad image?

Or does that plugin have at least any option to set how big pictures size and resolution can be? Without changing that option wordpress side to everyone to everywhere. Because administrators, authors and others are allowed to upload pictures (including big ones), but I really do not want let users add pictures too. Or if there is no other way to store and use pictures from images websites like imgur etc. then it would be nice to set some limits at least, so they will not upload some huge pictures.

They can use media images only if they are loggedin as user with file_upload capability, when using [adverts_add] as unregistered or Subscriber you will not be able to add Media Library images to description field.

There would also be additional problem with using the files, basically each user should have his own collection so other users cannot delete your files, this is just a one problem of many to figure out. To keep it simple if users want to have files in their ads they need to upload them.

I am planning to allow linking to video files in the gallery, so linking to images should be possible as well, but right now there is no ETA for this.