I use my laptop, MS Windows, Paint program to reduce pics, and add arrows, comments, etc.
I asked google: "iphone app to shrink a photos size":
Several iPhone apps are available to shrink photo sizes effectively. The Compress Photos & Pictures app allows users to reduce file sizes without significantly affecting image quality, with options to compress up to 90% or more while maintaining sharpness. It supports batch processing and saves compressed photos to a dedicated "Compressed Photos" album for easy access. Another option is Photo Compress - Shrink Pics, which enables compression of single images, multiple photos, or entire albums, with customizable JPEG compression strength and the ability to convert HEIC/HEIF files to JPEG. The Image Size - Photo Compress app lets users resize and lighten images with simple operations, including previewing changes and selecting output formats like JPEG or PNG. For users seeking a free, locally processed solution, Shrink.media is available as a free app from the App Store and compresses photos directly on the device without requiring an internet connection. Additionally, the Image Size app allows resizing using various units like pixels, centimeters, or inches, with a feature to preserve aspect ratio by tapping the chain icon. The Shortcuts app can also be used to create automated workflows for resizing images, which is useful for frequent users. These apps are compatible with iOS 13 or later, and some require iOS 15 or newer.
