Hello Timur,
Sorry for the confusion.
To paraphrase my sentence, if you don't create more than 300 responsive display ads (gallery ads) and the size of each ad's image doesn't exceed 1 MB (i.e., 2 MB (1 for marketing image and 1 for logo image) x 300 = 600 MB), then you will not face with any problems.
There're no published limitations about the total size of images allowed in an account that I'm aware of.
Or do you plan to upload images and use in other contexts than the responsive display ads?
I can check it with engineering but it would take some time.
Cheers,
Thanet, AdWords API Team