Most Indian exam portals want the photo between 20 and 50 KB and the signature between 10 and 20 KB, often at a fixed pixel size. This page caps the file at 20 KB; to hit an exact pixel size as well, choose Exact size (crop) under Resize and type the width and height from your notification (for example 140×60 for an SSC signature, or 200×230 for an IBPS photo).
At 20 KB you can expect roughly 300 to 450 px for a photo (a 3.5×4.5 cm passport photo at 200×230 fits easily), or a 300×80 px signature. The exact number depends on how much fine detail the image has: skies and plain walls compress well, foliage and fabric don't.
Tip: Scan signatures on plain white paper in good light. A grey or yellow background costs kilobytes that the ink then loses.