UPPRPB runs each recruitment on its own application portal, and the photo and signature limits are written in that portal's instructions. A recent portal used the sizes below; yours may differ.
UP Police constable, SI, jail warder and other recruitments have separate portals and notices. Never copy sizes from a different recruitment or an old blog post.
The UPPRPB website carries a notice/release section for each recruitment with the official advertisement and the link to its application portal. Start there, not from search results or forwarded links.
These rules change between recruitment years and notices. The current official notice and the upload screen of your form are the final word; this guide is only a helper, not an official recruitment page.
It depends on the recruitment. A recent UPPRPB portal asked for a 35 x 45 mm JPEG photo between 20 KB and 50 KB; read your own portal's instructions.
The same recent portal asked for a 35 x 15 mm JPEG signature between 5 KB and 20 KB. Confirm on your portal before preparing the file.
Only through the application link published on uppbpb.gov.in for your post. Avoid look-alike websites.