Idols and their studios often post entire "digital previews" of new photobooks on Twitter/X to drive sales. Search for #グラビア (Gravure) plus the tag #プレゼント (Present). You will often find 20+ high-res official images posted directly by the photographer.
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Despite the warnings, it's helpful to know where these searches lead so you can avoid them: Idols and their studios often post entire "digital
If you have your own high-quality images, you can use these services to get a physical photobook at no cost (usually only paying for shipping): Gravure Photobook Free