"Report to the People", a short story by William Sambrot, first published in the October 1953 issue of Bluebook; you probably read it in Sambrot's 1963 collection Island of Fear.
The story is about a scientist that invents a new telescope lens that lets him see aliens on the moon (I think). He brings his new lens to a "friend" that he has known for many years, and tells him all about it. His "friend" turns out to be an alien in disguise.
The story is narrated by the inventor's alien "friend":
""Let me get this straight," I put in. You invented some way of making glass for the lenses of microscopes or cameras?"
"Anything that requires the focusing of light," he said. "Coupled with my new grinding methods, the results are unbelievable." He sagged in the chair, and suddenly his face was weary. "I made several excellent reflectors and telescopes before I applied for the patents." He smiled wryly. "It's a good thing I did. At least I got a few good shots before they moved in."
[. . . .]
He pointed a long finger at the array of pix on my desk. "Those first three shots were taken with my fourteen-inch camera. Mars. The others are later shots, taken with the twenty-four incher. Remarkably good close-ups considering atmospheric problems at the time. Brings the surface of the planet to within a quarter of a mile."
"Did you say Mars?" I said. I felt the first crawling in my stomach as I searched his face intently. He seemed sane, but Mars.
"Imagine what abysses of space I could penetrate with even so small a lens as forty inches," he said somberly. "But they're afraid of us. They hold my patents, and they're too entrenched for us. Too clever."
I stared at the pictures again. Not submarines, but spaceships, Masterson was saying. Not undersea fairy castles supported by the dense water but needle-pointed towers of Martian civilization, with no heavy gravity to tumble them to the red ground.
Martians on the moon too:
He nodded impatiently. Remember those pictures released last year in that picture magazine, showing the moon from a distance of two hundred miles—blurry, with jagged shadows and deep black pits?" His lips twisted in disgust. "Faked. Every damn bit of it. The two-hundred incher on Palomar, bad as it is, is good enough to pick up anything on the moon over nine feet high!" He slipped another picture out of the envelope and tossed it to me.
The first thing ai noted were the contrasts. Blinding white and inky shadows. Anything in the shadows was cut off, so that I had a little trouble at first making out just what the picture depicted. Gradually things came into focus. And I mean things. Great spidery ramps, like infinitely high shoot-the-chutes at the beach. More of the submarine-looking objects, poised at the top of one of the great swooping ramps. Buildings, burnished and gleaming like miniature suns, were scattered all over in the background. And beings, plainly discernible, were swarming over the spaceship. Beings which looked remarkably human.
Then the alien uses a ring with a poison needle to poison the scientist when they shake hands.
"We never dreamed," I murmured, "that you had perfected your lens to obtain such results." I gestured to the heap of ashes. "But it doesn't matter anymore."
"I'll have to kill you," he whispered. His eyes flickered again. And again. His head rolled.
"You could have but no longer. Your handshake—the ring I wear." I showed him the tiny needle apparatus, although, even as I did so, it was too late for him. He slumped heavily to the floor and lay still. A most dangerous man. I was glad that at last we had the final proof that this particular menace was ended. I removed the negatives from his pocket and rang for assistance. I couldn't possibly have moved him myself.
Not in this awful gravity.
The poison doesn't kill the scientist right away, and he leaves his friend's office. As soon as the scientist leaves, the alien destroys the telescope lens.
Rather, he burns the photographs:
I held out my hand and he crushed it in a paw like a vise. He hesitated, shrugged, then walked out, a tall, somewhat noble figure. The moment the door closed I ripped the pictures into tiny shreds, piled them in a large bronze ash tray and set them afire. They were curling into black ashes when the door opened silently, and he bounded back in, his face white, his eyes blazing terribly.
I think that the scientist realizes that his "friend" is an alien at some point because he notices a "plastic surgery" scar behind his ear.
Thanks to a new technique, his "friend's" plastic surgery left no scar, but that's how the inventor recognized other Martians on Earth:
"Their ears," I said, interrupting his train of thought. "They don't have any ears."
"That's how I knew," he said absently, staring down at the close-up. "Plastic surgery. But their ears show a definite ridge, or line, where they join the head. If you're looking for it, you can spot it a mile away."