@RBnJrg...It's probably true that the "background-size" property would work for epubs and work on ADE. But "background-size" would not work for Kindle conversions because both the "background" property and the "background-size" property are not supported or recognized in the proprietary HTML used by Kindle format because Kindle devices only allow the background color to be controlled by the Kindle device user. This is also the reason why the "background" property is not allowed in Kindle format. Here is a list of Kindle supported html tags:
Kindle List of supported HTML Tags
I also have no idea how the OP is inserting his ebook images. How did he generate his epub file? Did he use a bad conversion? He hasn't said. And there are plenty of other converters out there besides Calibre.
From my own experience, ebook images can be easily inserted into an epub as full-page or smaller images without problems and without extra pages being generated in the epub. Such image pages, when generated properly, will display without problems in Sigils
Book View. After generating the full-page image epub file, all that needs doing is to ensure that the image is in a separate image file in Sigil's
Book Browser with all the appropriate entries in the opf manifest and
Images folder. Doing the latter will absolutely ensure that there is no extra spacing or blank pages after the displayed image.
As far as I can ascertain(without any html extracts to look at from the OP), the only way extra blank pages could be generated in the epub would be due to either incorrect setup in Calibre or incorrect setup or bad conversion on whatever epub converter he has used.
And as far as I'm concerned, there are too many unanswered 'what ifs' concerning the OPs image problem. We really don't have enough info in other words. And what would really help us solve his problem is to get some answers and feedback from the OP.